PSYU2247 Perception

Young's Colour Theory

"As it is almost impossible to conceive each sensitive point of the retina to contain an infinite number of particles, each capable of vibrating in perfect unison with every possible undulation, it becomes necessary to suppose the number limited..."

Detectability

- More intense the stimulus, the more likely you are to be able to detect it Detection Threshold (aka Absolute Threshold) - The intensity required for detecting a stimulus - e.g. how light does a circle have to be to be detected against a black background? - Lower threshold is better Sensitivity - The opposite of threshold (1/threshold) - Higher sensitivity is better

Proprioception/Kinaesthesia (mechanoreceptors)

- Muscles spindles - response to muscle length and rate of stretch - Golgi Tendon organs - respond to muscle tension - Joint receptors - respond to joint position

Noise

- Neural firing is stochastic - Precise firing rate determined mostly by stimulus but also by other random factors - Spontaneous activity - cells fire a little even with no stimulus

Plasticity

- Neural mechanisms are modifiable - Development - Recovery from brain injury

Which area of Psychology aren't impacted by perception?

- Neuropsychology - Clinical - Forensic

Positron Emission Tomography (PET) and Functional Magnetic Resonance Imaging (fMRI)

- PET: inject radioactive glucose and track it around the brain - fMRI: differences between oxygenated and deoxygenated blood - Slow responses

Illusions of depth

- Perspective (Ames Room) - Julian Beever pavement art - Steropsis - 3D movies - Autostreograms

Cortical Organisation

- Primary Somatosensory Cortex is a thin strip running over the top of the head (ear to ear) - Somatotopic Organisation - Bits next to each other on the body are represented next to each other in the cortex - Cortical Magnification - Some other body parts (lips, hands) occupy a much greater cortical area than others (torso)

Illusions of Motion

- Rotating snakes - Motion aftereffect ("waterfall illusion")

The Vestibular System

- Signals head's acceleration and inclination relative to gravitational vertical - 2 otolith organs - utricle and saccule - 3 semicircular canals - posterior, anterior or lateral (or "horizontal") - Each are filled with fluid and a small patch of sensory hair cells - Movements result in fluid flow, which displaces hair cells and leads to sensory responses

Complex Sounds: Adding Waves Together

- Sound waves are 'linear' i.e. they add together logically (sum the values at each point in time - Natural sounds are a collection of simple sine waves added together - The waveform of any sound can be expressed as a sum of sine waves with different freqs., amps. and phases - Just as you can add sine waves to make more complex waveforms, you can so the opposite too - Decomposing a complex sound into its component frequencies is called "Fourier analysis"

Selectivity

- Superficial receptors (Meissner/Merkel) respond best to light touch - Deep receptors (Pacinian/Ruffini) respond best to pressure and stretch

Somatosensory Transduction

- Tactile receptors - Selectivity - Proprioception/Kinaesthesia (mechanoreceptors) - Thermoceptors: "free nerve endings"

Illusions in Faces

- Thatcher Illusion

Illusions of Colour vision

- The Dress - Colour after effects

Principle Planes and Axes of the Human Body

- The body can move linearly along 3 possible axes: x, y and z - The body can also rotate around these axes: x (roll), y (pitch) and z (yaw) - These movements define 6 independent degrees of freedom - Natural movements combine 2 or more of these components - Stimuli for the vestibular system: - Linear acceleration along, or rotational acceleration around these axes - Tilt with respect to gravitational vertical

Discrimination Threshold

- The difference between two stimuli required for successful discrimination - Sometimes called the "just noticeable difference" (JND) - e.g. how different in brightness do 2 circles have to be before we can reliably tell them apart? - Lower is better

Properties of waves

- The waveform for a pure tone can be described as a sine wave - Critical features (or 'parameters') of a sine wave 1. Frequency 2. Amplitude 3. Phase

The Somatosensory System

- Touch is used to sense physical properties of surfaces such as texture, softness, size and shape - Thermoception is used to sense temperature - Proprioception is used to sense the position of body parts - Kinesthesis is used to sense the movement of body parts

Physiological Principles

- Transduction - Hierarchical processing - Selectivity - Organisation - Specific Nerve Energies - Plasticity - Noise

A better classification system

- Vision - Audition - The Chemical Senses Gustation Olfaction - The Body Senses Somatosensation Taction/Haptics Proprioception Equilibrioception

Thermoceptors: "free nerve endings"

- Warmth fibres - signal an increase in skin temperature - Cold fibres - signal a decrease in skin temperature Far less is known about proprio- and thermoceptors compared to tactile receptors

Plotting complex sounds

- We can re-plot the sound as amplitude vs. frequency called a spectrum - The component with the lowest frequency is called the fundamental frequency, which gives the sound its characteristic pitch - Harmonic frequencies are components of sound that have a frequency that is an integer multiple of the fundamental frequency

Organisation

- Within sensory brain regions there's often an orderly progression of stimulus preferences - Most "important" range of stimulus values is processed by a larger amount of cortex - "cortical Magnification"

Lesions

Animal Studies - Neurotoxins (specific pathway) or surgery (specific area) Human Neuropsychology - Usually diffuse damage, and often varying patterns of deficit Problems - Damage to fibres passing through can affect areas far from lesion - Brain recovers from damage "plasiticity" - Need to know the right test Transcranial Magnetic Stimulation (TMS) - Temporary - Magnetic field "knocks out" cells over a broad area - Temporally precise, spatially imprecise

Neuropsychology

Apperceptive/associative agnosia - inability to recognise objects - due to a perceptual problem, or higher? - see also agnosias in other senses (auditory, tactile etc.) - Phantom limbs/pains - Rubber hand illusion - Alien hand syndrome

Luminance

A measure of the brightness or lightness of a video image

Algorithm

A methodical, logical rule or procedure that guarantees solving a particular problem.

odorant

A molecule that can be detected by sensory receptors of the olfactory system.

linear perspective

A monocular cue for perceiving depth; the more parallel lines converge, the greater their perceived distance.

anaglyph

A stereogram in which the two photographs taken from adjacent camera positions are printed in contrasting colors and then superimposed; an observer who views an anaglyph with special glasses in which one lens filters out one of the colors and the other lens filters out the other color will see a single image in depth

Basilar membrane

A structure that runs the length of the cochlea in the inner ear and holds the auditory receptors, called hair cells.

Lesion studies (neurotoxic, surgical and human neuropsychology)

A surgical method in which a part of the animal brain is removed to study its effects on behavior or function.

Adaptation definition

A trait that helps an organism survive and reproduce

vergence

A type of eye movement in which the two eyes move in opposite directions; for example, both eyes turn toward the nose (convergence) or away from the nose (divergence).

Decibels

A unit of measurement of loudness

Focusing Errors

A) Emmetropia Normal refractive condition: appropriate focus B) Myopia (near- or short-sightedness) Focal length is too short Light is focussed in front of the retina Need concave corrective lenses C) Hyperopia/Hypermetropia (far- or long-sightedness) Focal length is too long Light focussed behind retina Need convex corrective lenses Presbyopia (old age) Inability to change accommodation Astigmatism Different focal lengths for different orientations E.g. OK for vertical lines, but myopic for horizontal lines

Crossmodal cueing - sounds influence visual detection

An auditory signal presented in the same location as the subsequent visual target leads to faster RTs and less errors for visual target detection. CONCLUSIONS: Irrelevant auditory stimuli can influence detection of a visual target

rod monochromat

An individual with no cones of any type. In addition to being truly color-blind, rod monochromats are badly visually impaired in bright light.

Vernier acuity

An observer's acuity for detecting the direction of small spatial offsets between collinear lines or edges.

How many senses?

Five? - sight (visual - eyes) - hearing (auditory - ears) - smell (olfactory - nose) - taste (gustatory - tongue) - touch (tactile, also haptic - skin) ALSO - balance (equilibrioception, vestibular system) - body awareness (proprioception, joints) - heat (thermoception, skin/internal)

Perceptual principles

Detectability - Measuring detection Sensory Magnitude - Measuring perceived intensity Discrimination - Telling things apart Adaptation - Consequences for detection - Consequences for perceived intensity and discrimination Measured with psychophysical methods - examples in practical 4 Many trial for accurate measurements (boring!) Results consistent between observers, with large effects - small n's In well designed experiments, it's hard/impossible to know what condition you're in - authors can be participants

Null direction

Excitation is smaller and delayed and inhibition is larger.

Cochlea amplifier

Expansion and contraction of the outer hair cells in response to sound sharpens the movement of the basilar membrane to specific frequencies. This amplifying effect plays an important role in determining the frequency selectivity of auditory nerve fibers.

Stroop effect

Explains the decreased speed of naming the color of ink used to print words when the color of ink and the word itself are of different colors.

Opponent processes

Explanation of color vision that emphasizes the importance of the apparently opposing pairs of colors: red vs green and blue vs yellow.

Prosapagnosia

Face blindness Impaired facial recognition ability (influenced by both genetics and the environment) Discovered in 1947 by Bodamer (noticed that many soldiers who had suffered injuries couldn't recognize loved ones

Detecting edges that aren't even there

Illusory contours (tut. 1) Presence of illusory edge could be signalled by interconnected hypercomplex cells Some cells in V2 respond in this way This allows detection of subthreshold edges

Inversion Effects

Image inversion affects matching (perception) and recognition (memory) performance for faces more than buildings, or any other object tested

Object Representation: Stage 3 - computationally difficult

Images of objects reflect both: 1. Intrinsic Factors Character of the individual object (shape, surface properties) 2. Extrinsic Factors - can change image of the object that are not related to its intrinsic properties • Viewpoint of observer • Lighting • Occluding objects • Background etc.

Intrinsic factors

Factors inside/related to the stimulus which affect perception

Extrinsic factors

Factors outside of the stimulus which affect perception

Cross Modal Mapping

Feed-forward networks are widely used in cross-modal applications to bridge modalities by mapping distributed vectors of one modality to the other, or to a shared space. The predicted vectors are then used to perform e.g., retrieval or labeling.

Fourier Filters

Filters separate things on the basis of a given property • E.g. A coffee filter separates things on the basis of particle size • Lets the liquid through (small particles), but "filters out" the granules (large particles) • "Low-pass filter" • Fourier filters allow certain frequency components of a sound to pass while blocking others • E.g. Sound travelling pass the head • Head obstructs high frequencies, thus acts as a low-pass filter

Microvilli

Fingerlike extensions of plasma membrane of apical epithelial cells, increase surface area, aid in absorbtion, exist on every moist epithelia, but most dense in small intestine and kidney

Phase locking

Firing of auditory neurons in synchrony with the phase of an auditory stimulus.

outflow theory

In contrast, outflow theory states that the motor signal sent to the eyes is monitored. A copy of this outgoing signal, which is called an efference copy or corollary discharge, is used to cancel the resulting movement of the image on the retina.

Test stimulus

In dark adaptation studies, the small spot of light for which the threshold is measured after the lights have been turned off.

Object representation

In object relations theories, the cognitive representations one has of oneself and others

Linear/Non-Linear Filters

In order to apply Fourier theory, we assume the filter is linear (i.e. it follows 3 rules) 1. Output of a filter must not contain any frequency which was not present in input 2. If amplitude of the input is changed by some factor, the output must also change by the same factor 3. Total output of multiple signals (A, B, C) must be equal to the output of A + B + C • Filters that violate these assumptions are called nonlinear filters. They often add distortions to a signal such as additional frequency components.

Qualia

In philosophy, private conscious experiences of sensation or perception.

Ganglion cells

In the retina, the specialized neurons that connect to the bipolar cells; the bundled axons of the ganglion cells form the optic nerve.

Hypercolumn

In the striate cortex, unit proposed by Hubel and Wiesel that combines location, orientation, and ocular dominance columns that serve a specific area on the retina.

Face matching task

In the test you will be asked to memorise a small set of faces and then recognise them. After completing the test, you will receive your score. You will be able to compare your score to those of other adults who have completed the test, which will provide an estimate of how good you are at recognising faces.

View-dependent theory

Incorporate extrinsic properties into the representation • Non abstract • Known objects stored as discrete prototypical forms/views

Physiology of motion LGN

LGN -6 "major" layers •M1-M2 Magnocellular •P3-P6 Parvocellular -but also 6 thin "minor" layers in between •K1-K6 Koniocellular - -Parvo •High spatial resolution/small RFs •Tuned to sustained stimuli (low temp. freq.) -Magno •Low spatial resolution/large RFs •Tuned to transient stimuli (high temp. freq.) -Konio Variable, but generally... •Very low spatial resolution/very large RFs •Tuned to intermediate temporal stimuli (mid temp. freq.) - •No actual motion selective cells yet, but Magno stream has cells selective for properties that are associated with motion

Waveform

Measurement of the distance between two wavelengths.

magnitude estimation (scaling)

Measures the relationship between objective (physical) intensity and subjective (perceived) magnitude of a stimulus

Illusions Explained

Simultaneous Lightness Contrast Illusion •Consider the activity of the two ON centre cells •Stimulation of the central (excitatory) region is identical •Only difference is that the cell on the left has less light in the surround •Less inhibition = more ganglion cell firing •Central square on the left is perceived as being brighter

Illusions of spatial vision

Simultaneous brightness contrast - Which square is lighter? Craik-O'Brien/Cornsweet Illusion - Which side is lighter? Adelson Checkerboard - Which square is lighter? Cafe Wall Illusion - Are these rows of bricks straight? The Fraser Spiral - or is it?

Rubber hand illusion

Subjects with normal brain function were positioned with their left hand hidden out of sight. They saw a lifelike _________ in front of them. The experimenters stroked both the subjects hidden left hand and the visible ______and with a paintbrush. The experiment showed that if the two hands were stroked synchronously and in the same direction, the subjects began to experience the ________ as their own.

Evidence for multisensory processing

Summary • Multisensory interactions are reflected behaviourally in the McGurk effect, crossmodal cueing and the ventriloquist effect • Multisensory signals influence identification, detection of external events and perceptual localisation How does the brain achieve multisensory perception?

Suprethreshold

Supra-threshold (or suprathreshold) refers to a stimulus that is large enough in magnitude to produce an action potential in excitable cells. ... Therefore, supra-threshold stimuli elicit action potentials

Amodal completion

Surfaces completing behind an occluding surface Surface is not seen but is "registered"

View-independent theory

Symbolic • Remove all extrinsic properties and build representations of objects in terms of component parts and relations between these a) Marr & Nishihara's 3D cone (1978) b) Biederman's geons (1987) - viewpoint independent

Gist Perception Wolfe and Horowitz (2017)

Syntactic - spatial layout • Semantic • Knowledge about the object provides an independent source of guidance • Useful 'priors' on where targets might be - toaster on a bench - cancer

Synesthetic congruencies affect multisensory interactions:

Temporal multisensory binding enhanced when cross-modally congruent (as compared to incongruent) pairs of auditory and visual stimuli > Stronger coupling synesthetically matched stimuli

Summary RHI Factors

Temporal synchrony important factor for body perception • Spatial correspondences less important (at least when hand is passive and up to distance of 45 cm: Zopf et al. 2010, Preston 2013) • Plausible and learned associations between visual information and multisensory signals important for body perception, e.g. visual form and orientation

Interaural Level Difference (ILD)

The ear furthest from the sound source lies in an 'acoustic shadow' cast by the listener's head - Intensity is lower at the further ear • Difference in intensity at each ear depends on frequency - For low frequencies, differences are small so not useful - For high frequencies, differences are large, so very useful • For a stimulus directly in front (or behind), ILD = 0 • Processed in Lateral Superior Olive in the brainstem

Tympanic Membrane

The eardrum. A structure that separates the outer ear from the middle ear and vibrates in response to sound waves.

Light Wavelength

The electromagnetic spectrum

Compression

The part of a longitudinal wave where the particles of the medium are close together.

Lateral Inhibition

The pattern of interaction among neurons in the visual system in which activity in one neuron inhibits adjacent neurons' responses.

Lateral inhibition

The pattern of interaction among neurons in the visual system in which activity in one neuron inhibits adjacent neurons' responses.

grey matter

The portions of the central nervous system that are abundant in cell bodies of neurons rather than axons. Unmyelinated.

Marr's primal sketch

The primal sketch is a symbolic, two-dimensional description of the significant grey-level changes in an image. Psychophysical evidence suggests a primal sketch in human vision, rather like that proposed by Marr, although different in many details.

Line of constraint

Those with a constrained vision favor solid empirical evidence and time-tested structures and processes over intervention and personal experience. Ultimately, the constrained vision demands checks and balances and refuses to accept that all people could put aside their innate self-interest.

Spectrogram of Speech

Time is plotted horizontally, frequency is plotted vertically, and amplitude is represented by the darkness of the plot ª Far more complex than simple sine waves!

Head shadow

attenuation of sound to one ear because of the presence of the head between the ear and the sound source

Terminal button

axon terminal containing synaptic vesicles

ordinal

being of a specified position or order in a numbered series

intrinsic

belonging naturally; essential

Spatial correspondence

between imagery and perception

Tritanomaly

blue-yellow discrimination altered

Inflow theory

brain receives input about rotation

magnetic resonance imaging (MRI)

brain-imaging method using radio waves and magnetic fields of the body to produce detailed images of the brain

Otolith Responses to Linear Head Movements

Utricle and Saccule - Either linear x-axis (forward) acceleration OR static head pitch (chin up) deflects the otolithic membrane, triggering responses in the underlying receptors (same is true for y-axis acceleration and roll) Why? They are equivalent stimuli!!! - Receptors are arranged on a horizontal otolithic membrane in the utricle, but on a vertical membrane in the saccule - Each respond to motion in various directions along the flat plane of the otolithic membrane - Between them, the pair of utricles and saccules will respond to linear acceleration or tilt along any axis

Physiology of motion V1

V1 (Primary Visual Cortex) -First stage of direction tuning, (the key to motion-selectivity) -Cell fires vigorously to one direction of motion, but remains at spontaneous rate when stimulated in the opposite direction -Small response to similar directions (tuning) -Applies to some simple, complex & hypercomplex cells

The Eye

Various parts: Cornea: The transparent "window" into the eyeball Pupil: The dark circular opening at the center of the iris in the eye, where light enters the eye Lens: Enables changing focus using ciliary muscles Retina: A light-sensitive membrane in the back of the eye that contains rods and cones, which receive an image from the lens and send it to the brain through the Optic Nerve Aqueous/Vitreous humor: The squishy bits. Not so interesting

Ventriloquist effect - vision affects auditory localisation

Ventriloquist effect: vision affects auditory localisation

Anatomical methods (dead brains)

Visible differences - white/grey matter Staining - Reveals axons/connections - Reveals cell body density and size - Reveals activity (cytochrome oxidase)

Depth and Stereopsis

Visual Cliff •Glass surface covers textures "clifftop" and the "void" •Enticed by rattle/toy •Infants reluctant to cross the void •Implies depth perception, but not necessarily stereopsis •Random Dot Stereograms (RDS) are only interesting after about 4-6 months (no other depth cues present)

temporal synchrony

Visual motion of mouth moving matches auditory speech

Three Stage Model of Shape and Object Detection

Visual processing is hierarchical

Body perception is multisensory:

Visual signals from the eye about body form, orientation, location as well as touch Tactile signals from the skin about touch Proprioceptive signals from joints muscles, tendon and skin-stretchsensitive receptors about hand orientation and location

Trichromatic

Visual system with three types of photoreceptors.

Non-Invasive (mostly humans)

Visually Evoked Potential (VEP) and Magnetoencephalography (MEG) - Measures electric currents or magnetic fields from cortex with sensors on the scalp - But which cells are responsible - Fast responses

Light

Wave of Electromagnetic Radiation Periodic changes in electric & magnetic field Light has a set wavelength, measured in nanometres (10-9 or 1/1,000,000,000 of a metre) Rays Travels in straight lines at a constant very high speed Particles Discrete packets, or "quanta" Light particles known as Photons

Synesthetic congruency

We all have a tendency to 'map' certain stimulus features across the senses systematically • For example: we match a high-pitched sounds with a small bright object that is located high up in space • In synaesthesia such cross-modal mappings are more extensive - stimulation one modality leads to an unusual perceptual experience in another modality (e.g., a sound leads to a colour experience)

Scene Perception

We are experienced viewing scenes • Visual processing is fast • Scene categorisation in < 50ms • Based on holistic processing of global spatial frequency (gist) - edges, contrast, openness

Pitch Perception

What is 'pitch'? - Perceptual attribute of a sound that corresponds most closely to its frequency

Multisensory Body Perception

What is it? •Identify body and estimate current location and shape • This process has to be flexible and dynamic • Signals from different senses are combined

Colour opponency

What is the term that refers to that the centre and surround cones can be different types?

Vestibulo-ocular reflex

What reflex enables the eyes to remain focused on a target while the head is turning?

Herman grid

When a light grid is placed on a dark background, people see faint illusory blobs in the grid intersections.

Motion parallax

a depth cue in which the relative movement of elements in a scene gives depth information when the observer moves relative to the scene

apperceptive agnosia

a failure to understand the meaning of objects due to a deficit at the level of object perception

associative agnosia

a failure to understand the meaning of objects due to a deficit at the level of semantic memory

orbitofrontal cortex

a region of the brain in which impulses involving excretion, sexuality, violence, and other primitive activities normally arise

lateral superior olive (LSO)

a relay station in the brain stem where inputs from both ears contribute to detection of the interaural level difference

Preferential Looking meaning

a research technique that involves giving an infant a choice of what object to look at

Oculogyral illusion

after spinning around, people often experience paradoxical motion in which the world appears to be spinning, but visually remains in the same place

odours

airborne chemicals that interact with receptors in the lining of our nasal passages

fusiform face area (FFA)

an area in the temporal lobe that contains many neurons that respond selectively to faces

Piriform Cortex

an area of medial temporal cortex that is adjacent to the amygdala and that receives direct olfactory input

piriform cortex

an area of medial temporal cortex that is adjacent to the amygdala and that receives direct olfactory input

Superior olive

an early brain stem region in the auditory pathway where inputs from both ears converge

McGurk Effect

an error in perception that occurs when we misperceive sounds because the audio and visual parts of the speech are mismatched.

functional magnetic resonance imaging (fMRI)

an imaging technique used to examine changes in the activity of the working human brain by measuring changes in the blood's oxygen levels

Tritanopia

an inherited form of defective color vision in which hues with short wavelengths are confused; "blue" cones are either lacking or faulty

Deuteranopia

an inherited form of defective color vision in which red and green hues are confused; "green" cones are filled with "red" cone opsin

Protanopia

an inherited form of defective color vision in which red and green hues are confused; "red" cones are filled with "green" cone opsin

Critical period

an optimal period shortly after birth when an organism's exposure to certain stimuli or experiences produces proper development

bottom-up processing

analysis that begins with the sensory receptors and works up to the brain's integration of sensory information

Synthetic process

any production process in which resources are combined

synthetic process

any production process in which resources are combined

Orthonasal

arising from odor compounds traveling through the "external nares," or nostrils, to the olfactory bulb.

orthonasal

arising from odor compounds traveling through the "external nares," or nostrils, to the olfactory bulb.

Meatus

canal-like passageway

Auditory Nerve Fibres

carry impulses from the inner ear to the brain

Neurotransmitter

chemical messengers that cross the synaptic gaps between neurons

Chemoreceptors

chemical sensors in the brain and blood vessels that identify changing levels of oxygen and carbon dioxide

chemoreceptors

chemical sensors in the brain and blood vessels that identify changing levels of oxygen and carbon dioxide

Detail perspective

closer objects appear to have more details

Subtractive mixture

color seen as the result of the absorption of light; the colors of objects

Spectrum

colored band produced when a beam of light passes through a prism

Dual process theory

combines the trichromatic and opponent-process theories to account for the color transduction process

Age related macular degeneration

condition in which the center of the retina gradually loses its ability to discern fine details; leading cause of irreversible visual impairment in older adults

Transduction

conversion of one form of energy into another. In sensation, the transforming of stimulus energies, such as sights, sounds, and smells, into neural impulses our brains can interpret.

Transduction definition

conversion of one form of energy into another. In sensation, the transforming of stimulus energies, such as sights, sounds, and smells, into neural impulses our brains can interpret.

Strabismus

crossed eyes

Habituation

decreasing responsiveness with repeated stimulation. As infants gain familiarity with repeated exposure to a visual stimulus, their interest wanes and they look away sooner.

Astigmatism

defective curvature of the cornea or lens of the eye

utricle and saccule

detect linear acceleration and the effects of gravity

Conditioned Taste Aversion

development of a nausea or aversive response to a particular taste because that taste was followed by a nausea reaction, occurring after only one association

conditioned taste aversion

development of a nausea or aversive response to a particular taste because that taste was followed by a nausea reaction, occurring after only one association

Sensory bias

development of a trait to match a preexisting preference that exists in the population

Perceptual narrowing

developmental changes in which experience fine-tunes the perceptual system

yaw

deviate abruptly from a straight course; swerve; veer

Median plane

divides the body into equal left and right halves

Neural Impulse

electrical signal traveling down the axon

Neural impulse

electrical signal traveling down the axon

Spatial opponency

excitatory responses generated in one part of the retinal receptive field are opposed by inhibitory responses in another part

oculomotor

eye movement

Hypermetropia

farsightedness

Carbon Chains

form the skeletons of most organic molecules

carbon chains

form the skeletons of most organic molecules

posterior-anterior (PA)

from back to front, as in reference to the direction of an x-ray beam

Insula Cortex

lies medial to lateral sulcus

insula cortex

lies medial to lateral sulcus

"yes"-"no" paradigm

m

Ossicles

malleus, incus, stapes

Volatiles

materials that turn into gas at the surface

volatiles

materials that turn into gas at the surface

Detectability definition

measured in terms of probability and depends on decision-making processes as well as sensory processes

Oval Window

membrane at the enterance to the cochlea through which the ossicles transmit vibrations

Absolute threshold of sensation

minimum intensity of stimulus needed to detect a particular stimulus 50% of the time

Coherent motion

movement of particles in the same direction

Ciliary muscles

muscles which relax or contract and alter the shape of the lens

ciliary muscles

muscles which relax or contract and alter the shape of the lens

Myopia

nearsightedness

Feature detector

nerve cells in the brain that respond to specific features of the stimulus, such as shape, angle, or movement

Spontaneous activity

nerve firing that occurs in the absence of environmental stimulation

Inner hair cells

neurons in the organ of Corti; responsible for auditory transduction

Cold Fibres

neurons that respond to a cooling of the skin by increasing the production of neural impulses

Parvocellular

of or consisting of relatively small cells

parvocellular

of or consisting of relatively small cells

Contralateral

on the opposite side of the body from another structure

Ipsilateral

on the same side of the body

Nanometre

one billionth (10-9) of a metre.

Hemifield

one of two halves of a sensory field

Retinotopic

organized, like the primary visual cortex, according to a map of the retina

Somatosensory

our sense of touch, temperature, and pain

Part/Whole effect

part of a face is more easily recognized when presented in the context of a whole face than on its own

Retronasal

pertaining to behind the nose

retronasal

pertaining to behind the nose

Binaural

pertaining to both ears

Monaural

pertaining to one ear

primary gustatory cortex

primary site involved with the interpretation of the sensation of taste

Hierarchical processing definition

processing that occurs in a progression from lower to higher areas of the brain

Hierarchical processing

processing that occurs in a progression from lower to higher areas of the brain - Neural impulses travel "up" the system to the cortex - "Relay station" in the Thalamus (except for olfaction) - Higher cortical areas also involve lateral and feedback connections

Microvilli

projections that increase the cell's surface area

Receptor

protein that detects a signal molecule and performs an action in response

Thermoceptors

provide feedback on internal body temperature

Timbre

quality of sound

Muscle spindles

receptors sensitive to change in length of the muscle and the rate of that change

Cross Adaptation

reduced response to one taste after exposure to another

cross adaptation

reduced response to one taste after exposure to another

Linear

straight line

umami

taste for monosodium glutamate

Cross Fibre Theory

taste quality is carried by the firing pattern across many taste nerve fibres

Magnetoencephalography (MEG)

technique that measures brain activity by detecting tiny magnetic fields generated by the brain

Pareidolia

tendency to perceive meaningful images in meaningless visual stimuli

Discrimination Threshold definition

the ability to distinguish the difference between two stimuli

Scotopic vision

the ability to perceive visual stimuli in near darkness due to the activity of rods

Photopic vision

the ability to perceive visual stimuli under bright light conditions due to the activity of cones

Pupil

the adjustable opening in the center of the eye through which light enters

Cortical magnification

the amount of cortical area devoted to a specific region in the visual field

Intensity

the amount of energy in a light or sound wave, which we perceive as brightness or loudness, as determined by the wave's amplitude

The Barberpole Illusion and Terminator Motion

•Ambiguous signals in centre of pole (the "aperture problem") •Signals at edges ("terminators") are unambiguous (2D features) •Two different directions ( & ) •More numerous signals win •Terminator motion signals "fill in" for the ambiguous central motion signals •Ambiguous signals in centre of pole (the "aperture problem") •Signals at edges ("terminators") are unambiguous •Two different directions ( & ) •More numerous signals win •Terminator motion signals "fill in" for the ambiguous central motion signals •Indentations make terminators move at 45º. Whole pattern appears to move at 45º

Synapse

the junction between the axon tip of the sending neuron and the dendrite or cell body of the receiving neuron

Retina

the light-sensitive inner surface of the eye, containing the receptor rods and cones plus layers of neurons that begin the processing of visual information

Detection Threshold

the lowest concentration at which an odorant can be detected

Residue pitch

the pitch heard in a complex wave as a result of beats rather than resolvable harmonic components

Blind Spot

the point at which the optic nerve leaves the eye, creating a "blind" spot because no receptor cells are located there

Psychophysics

the study of relationships between the physical characteristics of stimuli, such as their intensity, and our psychological experience of them

Rate code

the system by which information about different frequencies is coded by the rate of firing of neurons in the auditory system

Flavour

the taste of a particular type of food or drink

flavour

the taste of a particular type of food or drink

Texture gradient

the tendency for textured surfaces to appear to become smaller and finer as distance from the viewer increases

Orientation tuning

the tendency of neurons in striate cortex to respond optimally to certain orientations and less to others

Lens

the transparent structure behind the pupil that changes shape to help focus images on the retina

Computerized Tomography (CT)

the use of a device that employs a computer to analyze data obtained by a scanning beam of X-rays to produce a two-dimensional picture of a "slice" through the body

Synaesthesia

the use of one kind of sensory experience to describe another

transcranial magnetic stimulation (TMS)

the use of strong magnets to briefly interrupt normal brain activity as a way to study brain regions

Pinna

the visible part of the ear

Otolithic membrane

thick, gelatinous, glycoprotein layer located directly over hair cells of the macula in the saccule and uricle of the internal ear

Semicircular canals

three canals within the inner ear that contain specialized receptor cells that generate nerve impulses with body movement

Amygdala

two lima bean-sized neural clusters in the limbic system; linked to emotion.

amygdala

two lima bean-sized neural clusters in the limbic system; linked to emotion.

magnocellular

two ventral layers - large cells, large receptive fields

Hz (Hertz)

unit for frequency

Nanometres

unit of length: 1 nanometre = 0.000 000 001 metre

Masking

using a second sound, frequently noise, to make the detection of another sound more difficult

illusory contours (subjective contours)

we see edges even though they are not physically present in the stimulus

Sensory Tuning

when the sensory perception of an animal is most sensitive to a particular (adaptive) range of stimulus.

Macula

yellowish region on the retina lateral to and slightly below the optic disc

The Ear

ª 3 parts ªOuter Ear ªPinna, Meatus ª Middle Ear ªOssicles ªTympanic Membrane (ear drum) ª Inner Ear ªCochlea

Transduction: Inner Hair Cells

ª 3500 inner hair cells protrude from the basilar membrane. ª Fluid displacement causes vibration in basilar membrane ª This deflects the stereocilia of inner hair cells, generating impulses ª The base of each inner hair cell makes contact with afferent fibres of the auditory nerve (50,000 nerve fibres).

Outer Hair Cells & the Descending Auditory Pathway

ª Descending fibres run from auditory cortex to cochlea, with synapses in reverse order to ascending projections. ª Descending projections may be involved in auditory attention and outer hair cell amplification functions. ª More outer hair cells (3 rows) than inner hair cells (1 row) yet only 5-10% of them send signals "upwards" ª Many outer hair cells receive impulses from higher areas, and respond by changing their length - known as their "motile response" ª This serves as a "cochlear amplifier", making the early auditory processes highly non-linear

Olfaction & Memory

•An account of olfactory perception needs to incorporate memory •Smells presented together acquire properties of each other (Stevenson, 2001) -Reduced discriminability •Wine tasters can discriminate up to 100,000 odour objects (i.e. odourant mixtures) •Case of patient HM -Brain surgery for intractable epilepsy •Epithelium & olfactory bulb intact, but piriform cortex removed -Severe disruption of memory -Also inability to discriminate odours unless they differ in intensity (Eichenbaum, 1983)

Analysis vs. Synthesis

•Analysis -The percept can be broken down into its separate components -e.g. hearing the individual notes in a musical chord •Synthesis -The combination of components forms a new perceptual whole that can't be broken down -e.g. Red + Green = Yellow, but yellow doesn't look like either

Anisometropic Amblyopia

•Anisometropia - unequal focussing in the two eyes •The 2 retinas receive different inputs •Few cells selective for high spatial frequencies for the poorly focussed eye •Low acuity for poorly focussed eye •Few binocular cells •This is "amblyopia" (aka lazy eye) - literally "blunted vision"

Intersection of Constraints (IOC)

•Any closed object must have edges at different orientations •Each oriented line has its own "line of constraint" (LOC) •LOCs intersect at a point representing the velocity of the object

Inner Hair Cells: Place and Frequency Codes

ª Place code ª Hair cells have a "characteristic frequency" to which they respond best, determined by the part of basilar membrane to which they are connected. ª Sound frequency can be encoded by the region of basilar membrane to which the most active cell is attached. Frequency (rate) code ª Inner hair cell impulses are timed to coincide with a certain phase of the wave ("phase locking"), at least for low frequencies ª So the response rate of a particular nerve fibre should reflect the frequency of the signal.

Summary

ª Three critical parameters of sound wave are frequency, amplitude, and phase ª Complex sounds consist of a collection of simple sine waves at different frequencies (Fourier theory) ª Spectrograms can be used to visualise frequency content over time ª Peripheral auditory system consists of the outer ear, middle ear, and inner ear (cochlea) ª Hair cells at different places in the cochlea encode different sound frequencies (frequency-to-place conversion). ª Information is then sent through the auditory nerve to the brain (ascending auditory pathway) and back down to the cochlear (descending auditory pathway

Auditory Cortex

ª Tonotopic Organisation ª Primary auditory cortex is organised in terms of sound frequency - there is an orderly progression of cell's preferred frequency across the cortex.

Outer Ear

ªPinna: the flexible flap on the outside of the ear. ªFocuses sound waves into the ear canal (meatus). ªShape & size of outer ear have the effect of amplifying medium sound frequencies (1500-7000 Hz)

Michelson Contrast

• (L_max - L_min)/(L_max+L_min) - L_max and L_min are measures of luminance • describes the threshold contrast of a subject (?) - measured SDT observation of gratings (e.g. can you see the grating)

Integration Across Orientation

•Aperture problem also applies to sections of 2D objects •As before there is 180° directional ambiguity - all possible motion vectors terminate along one "line of constraint" (LOC) •LOC is parallel with the 1D feature, and perpendicular to shortest possible motion vector

Summary Multisensory Body Perception

• Body self-perception is not static, but flexible and constantly updated • Plasticity is important to deal with changes to the body (e.g., movement, growth, injury, tools) • The processing of multisensory signals is crucial for body selfperception • Experiencing multisensory synchrony and the plausibility that the viewed object could be one's own body enable identification and localisation of one's body

Contrast Sensitivity Function (CSF)

•Are we better at seeing high SF, or low SF patterns? •Use 2AFC method - -"Which interval contained the grating, 1 or 2?" -Plot % correct as a function of contrast -Threshold is 75% correct -Measure at various SFs •Divide 1 by the thresholds to yield sensitivity •This is the contrast sensitivity function (CSF)

Motion Parallax

•As the observer moves, stationary objects at different depths move (relative to the observer) at different velocities •Imagine staring off into the distance through a train/car window (video) -Closer things move more quickly -More distant thing move more slowly •Monocular, Visual, Metric •Not strictly pictorial (requires motion)

Height in the Visual Field

•Assuming that things generally tend to rest on the ground plane, things higher up in the visual field are often more distant •Note also the apparent size of the three men in this figure (more on apparent depth and apparent size later) •Monocular, Pictorial, Visual, Metric

Scotopic (night time) Colour Vision

•At low luminance (e.g. night vision), cones are not sensitive enough to respond - rods only •Our colour vision with rods alone is poor: almost non-existent •Why? -"Principle of Univariance"

Sensitivity to Contrast

•At this early stage of the visual system we can see that contrast (rather than luminance/brightness) is given priority •Most visual cells increase activity in response to increases in contrast •What is contrast? -The difference in physical luminance, (taking into account the overall luminance levels) -0-1, or sometimes a %age (0-100) Michelson Contrast (C) formula:

Infant Face Vision

•Babies seem to be born ready to process faces -Detection of Faces: Infants (some <1hr old!) have viewing preference for faces over "scrambled" faces -Recognition/Discrimination of Identity: 2-day olds track picture of their own mother vs. other plausible mothers

Colour Deficiency

•But some people are truly colour blind (i.e. can only tell light from dark) - -Monochromats •Cone monochromats have only one type of cone & lack colour vision day & night •Rod monochromats have no cones at all Highly sensitive - need dark glasses in daylight - -Cerebral Achromatopsia Damage to area V4 can cause complete "colour blindness"

Physiology of Opponent Processing

•Cells have been found in LGN and V1 which show antagonistic cone inputs •Some also show a centre-surround arrangement - "double opponent" cells •R/G cells are Parvocellular, B/Y are Koniocellular, B/W (luminance) are Magnocellular •V1 hypercolumns contain "blobs": cylinders where opponent colour cells are located •More detailed model than the ice cube model in spatial vision lecture

What is Motion?

•Change of position (displacement) over time -Speed = Distance/Time •OR, if you're into gratings, etc. -Speed = Temporal Freq./Spatial Freq. -Note: Temporal Frequency (TF) is like Spatial Frequency (SF) but works across time rather than space -The number of cycles of light to dark and back again in 1 second is the TF

Transduction & Early Physiology

•Chemoreceptors are found on the tips of microvilli, projecting from the end of taste receptor cells • •One taste bud is a clump of 50-150 receptor cells -~5,000-10,000 taste buds -Mainly on tongue, but also elsewhere in mouth & throat -Taste receptor cells last ~10 days - •Free nerve nerve endings -Responsible for signalling the spiciness of foods like chilli, or the "cool" of menthol

Preventing Amblyopia

•Chicken or the egg? Eye problem first or neural problem first? •Monkey experiment: -Deliberately blur visual image -Anisometropic amblyopia still develops -=> It's due to the input, not a weakness of the cells -Effect limited to cortical cells •Remedy in critical period - patch good eye to force use of other eye •Up to 2 hours/day, up to 6yrs to work, earlier the better •Stereopsis (requires eyes to work together) may remain compromised

Colour Matching

•Colour Matching Experiments (Young, 1802) -To match any single, pure l of light (i.e. create a metamer), humans need 3 (or fewer) "primaries" of adjustable intensity -Any 3 ls of light can be used (so long as they are suitably different) •Like your TV screen, or the projector in lecture theatres •Most use single ls that appear Red, Green & Blue -From this we infer that most observers have 3 cone types

Trichromatic Metamers

•Colour encoded by the pattern of relative activation of each channel •Like population coding in spatial vision, olfactory perception, etc. •Consider the cone activation for 650nm (red), 550nm (green) and 580nm (yellow) •Consider the cone activation levels if red and green ls were presented together -Sum the Short l cone response to red & to green, then do the same for the other two cone types •Pattern for red + green presented together is the same as for yellow presented alone

Identification of Unfamiliar Faces

•Eyewitness testimony is often unreliable, especially when it involves unfamiliar faces •Witnesses are influenced by external features •External features are easiest to change, and hence eye witnesses are easily fooled •"Have you seen this man?" Photos on TV crime shows are only likely to be useful for recognising people already known to you (dob in your family members or neighbours)

Face Perception and Familiarity

•Familiar faces -Recognition or matching performance good -Independent of •Viewpoint •Lighting •Expression • •Unfamiliar faces -Recognition or matching performance poorer •Image specific

Familiar Size

•Familiar objects that have a stereotypical size can appear further away when their retinal image is smaller •For objects of constant size (i.e. almost all objects), its retinal image size varies with distance •Simple relationship (e.g. half the distance = double the retinal image size) •Monocular, Pictorial, Visual, Metric

Binaural Sound Localisation

• Both ears can receive differences in sound waves depending on the sound source location • They differ in... - Time of arrival to each ear (Interaural Time Difference - ITD) - Intensity or 'Level' (Interaural Level Difference - ILD) • Duplex theory - ITDs good for localising low frequency sounds - ILDs good for localising high frequency sounds • Direction of sound source is specified by an azimuth angle relative to straight ahead

Interaural Time Difference (ITD)

• Difference in time of arrival at each ear depends on azimuth • ITD = time(L ear) - time(R ear) • Maximum ITD is ~650 microseconds for a stimulus directly to the right or left • For a stimulus directly in front (or behind), ITD = 0 • Any given time difference could be either of two possible azimuths (e.g. 0.4msec delay could be 50° or 130°) • Processed in Medial Superior Olive in the brainstem

And then it starts getting really complicated...

•...but let's not worry about that too much! •Generally, as we move further from V1, areas become more selective •Hierarchies •BUT many connections are lateral or backward

Selective Rearing Expts

•AKA "Visual deprivation experiments" •Change the visual stimuli that animals (often cats) receive from birth •E.g. monocular deprivation •Suture one eye shut •Measure ocular dominance of adult cat's cells in primary visual cortex •Many cells driven by inputs from the eye that is stimulated •Virtually no cells driven by the closed eye, or binocular cells •Environmental deprivation •Raise kittens in a specific environment e.g. exclusively vertical patterns •Adult cat is effectively blind to horizontal contours •Measurement of orientation preference in adult cat visual cortex cells shows bias towards environmental stimuli •Timing of deprivation vital •Critical Period Deprive one eye, then another within

Centre-Surround Antagonism

•AKA Lateral antagonism, Lateral inhibition, Spatial opponency •Ganglion cell RF has 2 concentric areas •2 types of cell •ON Centre -Light falling on the inner portion causes an increase in ganglion cell activity -Light on outer portion decreases ganglion cell activity -Final response level is a result of this excitation & inhibition •OFF Centre -Light on inner portion causes a decrease -Light on outer portion causes an increase Note: "0" on this diagram refers to baseline or spontaneous activity

Acuity vs. Vernier Acuity

•Acuity - the highest SF (i.e. narrowest stripes) that can be seen •Vernier acuity - the smallest displacement of a line that can be detected •Babies start off having very poor Vernier acuity compared to acuity •Vernier acuity grows much faster, and eventually overtakes acuity •Adults have much better Vernier acuity than grating acuity (approx. 10x)

Non-nutritive Sucking

•Adapt pacifier with a pressure transducer to measure sucking •Newborns suck their thumbs, or pacifiers, when bored •When distracted with a new stimulus, they pause sucking •If they are presented with a visual stimulus that they can't see (e.g. too high in SF, or too low in contrast), then the sucking response may increase

The Motion Aftereffect (MAE)AKA the Waterfall Illusion

•Adaptation: prolonged exposure to a particular stimulus -Increased ('elevated') detection thresholds for similar stimuli e.g. adapting to low spatial frequency (fat) gratings makes it more difficult to detect low-contrast gratings with the same spatial frequency (SF) -Reduction of perceived intensity of stimulus e.g. mid-contrast gratings with same SF now seem to be low contrast -A biased (often opposite) percept e.g. mid SF gratings now look higher in SF •MAE is a biased percept as a result of adapting to a motion stimulus -Look at motion in one direction, then stationary things appear to drift in the opposite direction

Additive Colour Mixtures

•Adding various pure ls of light together forms new colours -Short + long (blue + red) light -> purple -Short + medium (blue + green) light -> turquoise -Medium + long (green + red) light -> yellow -Short + Medium + long light -> WHITE •The ls of light have not changed •These are additive colour mixtures •"But hang on - when I mix paints, it comes out as a dark mess!" •That's because mixing paints is different - it is a subtractive process

Autostereograms (Tyler, 1979)

•Also "SIRDS" - Single Image Random Dot Stereograms •One image with pattern that repeats horizontally •Adjust vergence to align neighbouring regions •Horizontal distance between repeating items varies - introduces disparity

Binocular Disparity

•Also "retinal disparity", occasionally "binocular parallax" [Note: "dis" + "parity" = "not" + "equal"] -For any two objects at different depths, the relative position of their images is different in the two eyes -First formally described by Wheatstone (1838) -Small depth difference => small disparity -Large depth difference => large disparity Binocular, Non-pictorial, Visual, Metric

Sorry: what are filters again?

•Filters separate things on the basis of a given property -E.g. Coffee filters separate on the basis of particle size Lets the liquid through (small particles), but "filters out" the granules (large particles) •In audition, auditory nerve fibres filter sound on the basis of frequency •In vision, cells act as filters for many different stimulus properties -They let the neural signal through for stimuli that they are tuned to, and filter it out for others -E.g. Orientation filters, size (or spatial frequency) filters, colour (light wavelength) filters (see lecture on colour vision) etc.

Corresponding Points

•Imagine that both eyes are looking at (fixating) a cross a couple of metres away -Cross falls on the fovea in each eye -L & R half-images of the cross fall on corresponding points of each retina (i.e. they are in the same place) - •A circle is at the same distance as the cross and just to the left -Half-images fall just to the right of the cross on each retina - also corresponding points - •For the triangle behind the cross... -Half-images fall just to the left of the cross on the left retina but a long way to the left on the right retina -Non-corresponding points -Object has a binocular disparity

Faces

•Important social stimuli •We can remember thousands •...and identify them despite changes in lighting, viewpoint, expression, hairstyle, glasses, etc. •We can perceive race/sex/identity/emotion etc., independently of each other •We see can see/recognise a face, given only minimal information •Even if it is not actually there! (Pareidolia)

Neurophysiology of face recognition

•Inferotemporal cortex (IT) contains cells that respond selectively to complex shapes, objects or faces (see R/G/B areas) -Single unit studies in monkeys •A subsection is particularly selective for faces (in normal humans), and has been named the "Fusiform Face Area" (FFA) marked in green -fMRI studies

Why is multisensory integration important?

•Integrating visual and auditory signals is important to understand speech, particularly in... ˗ noisy environments ˗ hearing impaired people ˗ unfamiliar languages ˗ & building speech recognition systems Integration of mismatching information can change perception => McGurk effect

Why is multisensory integration important?

•Interactions between the senses direct our attention: ˗ A sound can direct visual attention to a specific location (e.g., alarms) ˗ A movement can help localise the source of a sound (e.g., car approaching) ˗ A tactile sensation can direct visual attention to the source

Inversion Effects explanation

•Inversion disrupts holistic processing -Poorer matching & recognition for inverted vs. upright faces •Effect is larger than for other objects (houses, aeroplanes, etc.) •Matching/recognition of parts is not affected as much -No face composite illusion with inverted faces -No whole/part effect with inverted faces •Inability to extract expression (Thatcher Illusion) •Inverted faces are treated like other objects

The Thatcher Illusion

•Inversion results in many face processing deficits •e.g. Expressions are more difficult to discern in inverted faces •There are other surprises too! •Has anyone noticed anything strange about this face?

Active vs. Passive Vision

•Is proper visual input to both eyes in the critical period enough? •Role of interaction with visual environment - the "kitten carousel" •Kitten in carousel yoked to collar of active kitten •Measure depth perception - carousel kitten poor

What is "out there"?

•Largely the same as for olfaction, but chemicals go further into our bodies • •Molecules dissolve in saliva & bind with receptors

Part/Whole Effect

•Learn whole faces by name (e.g. Larry) •Later, choose Larry's nose (from 2 alternatives) -Whole face condition (Larry's face, either with Larry's nose, or another nose) -Isolated part condition (Larry's nose vs. another nose) •Participants do better when presented with whole faces (where only the nose differs)

Presbyopia

•Lens loses flexibility -Decrease in accommodation (complete loss by ~55yrs) •Corrective lenses required depends on fixed state of the lens -May need glasses for distance/reading -May need bifocals or varifocals (aka progressive lenses)

Accommodation

•Lens must change shape to maintain a sharply focused image as object distance varies (see blur) • • •State of ciliary muscles controlling accommodation offers a cue to depth -While fixating a distant object (left) the ciliary muscles are relaxed and the lens is relatively thin -While fixating a near object (right) the ciliary muscles are tensed to allow the lens to take on a thicker shape • • •Monocular, Non-pictorial, Oculomotor, Metric

Attached Shadow

•Light reflectance patterns reveal the angle of surfaces with respect to the light source and observer •E.g. Circular regions appear concave or convex, depending on pattern of shading •Rotating 180º reverses the perceived depth •Again, assume light source is uniform, and located above •Monocular, Pictorial, Visual, Metric

Size Channels ?

•Like orientation tuned cells, there are cells in V1 tuned to the width of bars/stripes •There is also a size aftereffect •Adapting to fat (thin) stripes makes medium stripes look thin (fat) •Explanation is the same as the tilt aftereffect (population code for size)

Three Cone Types

•Long (peak 560 - reddish) •Med. (peak 530 - greenish) •Short (peak 420 - blueish) -Blue light is often blurred •Few in the fovea •More sparse • •Images of human trichromatic cone "mosaic"

Physiology of Motion Perception

•Lower vertebrates -Retinal motion cells! •E.g. Frog, Rabbit •Primates (incl. humans) -Magnocellular Pathway: major forward connections - LGNm → V1(4Ca) → V1(4B) → V2(Thick Stripes) → MT+ •Also lateral & backward (feedback) connections

Physiology of motion MT+ (V5)

•MT+ (aka V5) -Many motion selective cells -Large receptive fields -Preferred directions represented in columns -Microstimulation influences direction judgements -Cells respond to relative motion/optic flow/self motion -Pursuit eye movement cells -MT lesions cause akinetopsia (e.g. patient LM) Can perceive change of position/size, but no perception of motion per se Motion looks like a collection of 'snapshots'

•With a 2-cone system...

•With a 2-cone system... •...we could match any given l by adjusting the intensities of almost any two other ls (metamers) •...there would be a single l that appears grey. This is known as a "neutral point", where the firing of both channels is equal •For the 2 receptor system on previous slide, the "mid" l would be perceived as neutral (grey) •Ratio of responding is the same as when all ls are present • •Are these things true for humans? •NO except for some unfortunate observers, e.g. your lecturer!

RDS & Cyclopean Vision

•With the RDS, Julesz introduced a new phenomenon: Cyclopean Vision •Left eye sees a bunch of dots •Right eye sees a bunch of dots •When the two are presented together, we see two square regions (in depth) that were not present in either half-image •These squares are described as cyclopean - they emerge only after binocular combination

Are Faces "Special" ?

•i.e. are they dealt with by the visual system in a different way to other objects ? •YES! (probably) -Infant Vision -Holistic Processing •Composite Face Effect/Chimaeras •Part/Whole Effect •Inversion -Neurophysiology/Neuropsychology •Inferotemporal cortex & the FFA •Prosopagnosia

Face Perception & Memory

•Many face processing studies are principally concerned with memory (Cognition) -Recognition/recall tasks: a) Learning Phase: Exposure to a set of faces, with instructions to remember them b) Retention interval (variable length) c) Test Phase: View again, along with never-seen-before faces. Qu: "Old or new?" •To remember something, we have to be able to encode it first (Perception). Some studies investigate this aspect of face processing per se. -Matching tasks (e.g. view simultaneous face pairs (or arrays): "Do they match?") •Here we'll cover the perceptual aspects (but also some memory phenomena).

Hierarchies: Cortical Physiology

•Mitral cell axons connect directly to primary olfactory cortex (aka piriform cortex) & amygdala -No thalamic relay (although signals do go to the thalamus later) -Mitral cells are in the same relative position in all animals of a species (Smith, 2000) - •Strong emotional impact of smell may be due to its direct connection to the amygdala

Subtractive Colour Mixtures

•Mixing paint is a subtractive process •Most paint reflects more than just a single, pure l of light •Blue paint reflects mainly short ls (blue) of light, but also some of the neighbouring ls (purple & green) •Yellow paint reflects mostly yellow light, but also a bit of green & orange •Putting both together, the new patch reflects only green •The more colours of paint you add, the more light is absorbed/subtracted and the darker the patch looks

What is "out there"?

•Molecules/Chemical compounds •If they are released into a gas, they're called "volatiles" •If they smell, they're called "odourants" -Mostly organic compounds (carbon chains) •Most odours that you know (e.g. cheese, coffee) contain a mixture of many, many odourant chemicals

Properties of Depth "Cues"

•Monocular vs. Binocular -Could you get this info with only one eye? •Pictorial vs. Non-pictorial -Could the info be available in a photograph? -Pictorial ≈ Monocular •Visual vs. Oculomotor -Visual: info comes purely from the retinal image -Oculomotor: info comes from the eye muscle signals •Ordinal vs. Metric -Does the info simply tell us which object is closer (ordinal), or does it tell us by how much (metric) ?

Types of Depth Cue

•Monocular vs. Binocular -Could you get this info with only one eye? •Pictorial vs. Non-pictorial -Could the info be available in a photograph? -Pictorial ≈ Monocular (except for Motion Parallax, which requires movement) •Visual vs. Oculomotor -Visual: info comes purely from the retinal image -Oculomotor: info comes from the eye muscle signals •Ordinal vs. Metric -Does the info tell simply tell us which object is closer, or does it tell us by how much?

Yellowing

•More blue light absorbed •Less able to tell dark blue from black

Advantages of 2 Eyes

•Most animals (certainly vertebrates) have 2 eyes • •Some are placed laterally: an eye each side of the head -Generally tend to be prey animals (duck, rabbit, etc.) -Visual fields overlap only minimally -All-round coverage of the world to detect predators • •Others are frontal -Generally tend to be predators (cats, owls, etc.) -Visual fields overlap considerably -Some areas of space not covered at all

The Barberpole Illusion

•Motion appears to be along the long-axis of the figure... •Even when there are TWO long axes! -This "Barbercross" is a single oblique grating seen through a cross-shaped window -Motion upward along vertical arm -Motion rightward along horizontal arm

Stroboscopic (Apparent) Motion

•Motion on TV is illusory -There is no motion, just several discrete positions over time -Given the right distance moved and frame rate, it looks like motion (demo) - •Why does it look so real? -Not persistence of vision •Blurring has nothing to do with it - in fact moving images often look sharpened, not blurred! -Apparent motion stimulates motion detectors in the same way as real motion -e.g. Reichardt detectors do not care what happens in between the two receptors

Visual Development Summary

•Nature AND nurture -Nature: Newborns have rudimentary vision - some ability to process visual stimuli -Nurture: Plenty of room for improvement of visual capabilities -Different visual abilities start/finish developing at different times and at different rates (NB: Peak contrast = lowest contrast detected across all SFs) •How/why does this development come about? -Just a natural improvement as the anatomical structures reach maturity? Or something else?

How to Simulate Stereoscopic 3D (from 2 flat images)

•Need 2 images/photos taken approx. 6.5 cm apart •Display one to each eye •Many methods of presenting the images & ensuring that each eye receives the appropriate image: -Mirror stereoscopes (e.g. Wheatstone stereoscope) -Prism/Lens stereoscopes (e.g. Viewmaster/Brewster stereoscope) -Anaglyphs (Red/Green or Red/Cyan lenses, as used in prac 3) -Polarisation (e.g. 3D cinema) -Shutters (e.g. 3DTVs) -Vertically Interlaced Displays (Lenticular/Parallax Barrier) -Free Fusion (e.g. RDSs & Autostereograms, aka "MagicEye" pictures)

Development of Spatial Vision

•Neonates' vision is quite blurry -Inability to see fine detail (high SF) -Only coarse structure (low SF) is visible • •Visual acuity increases approximately linearly over the first ~3 years •This is confirmed when measuring the full Contrast Sensitivity Function (CSF) •Babies are less sensitive for all spatial frequencies •Approx. adult levels of (grating) acuity are reached around 8yrs But do all abilities develop at the same rate?

What is light?

•Newton's Prism Experiments •White light, passed through a prism, splits into a spectrum of different lights that appear coloured (refraction) •Repeat the process: no further decomposition occurs •Reverse the process: colours converge to form white again •"The prism does not destroy the character of light, it only reveals its components"

Snellen Acuity

•No information about thresholds for low & medium spatial frequencies •High contrast only •Tests resolution limit -High SF "cut-off" •Easy to cheat ! Need to measure CSF !

Aerial (Atmospheric) Perspective

•Not connected to linear/detail perspective •More distant objects tend to be -Lower contrast -Lighter -More blue •Particles in the atmosphere (gas, water, dust, etc.) fade the image by scattering light •Larger the distance => more scattering of light by intermediate particles •Contrast-depth relationship depends on local atmosphere •Monocular, Pictorial, Visual, Metric

Colour Constancy

•Objects generally look the same colour in a wide variety of lighting conditions •Land (1977) -Isolated coloured patch appears to change colour when lit by different wavelengths -When this patch is part of a Mondrian Pattern, it appears to be the same colour regardless of the illumination •Cells in area V4 appear to show this property - they exhibit colour constancy

Reflection of Light

•Objects... -...reflect light, or absorb (subtract) it -...appear to be... •...the colour of the light that they reflect •...black if they absorb lots of light at all ls, and reflect little •...white if they absorb little light, and reflect lots at all ls •...yellow if they absorb all else, and reflect only yellow (e.g. ~580nm)

Colour Opponency(Hering, 1872)

•Observations -When asked to select "pure" colours, people pick 4, not 3 -Humans describe the world using 4 colours •Reddish-blue, or yellow-green, but never reddish-green or blueish-yellow •Inference -Two opponent colour axes: red-green and blue-yellow •For full colour space, we need to include the black-white axis •Grey is neutral: neither red nor green; neither blue nor yellow; neither black nor white

Transduction & Early Physiology

•Olfactory receptor cells (chemoreceptors) found in the roof of the nasal cavity, in the olfactory epithelium •Odorant receptors (olfactory receptors) are on hairs projecting from receptor cells -500-1000 different receptor/receptor cell types -Renewed approx. every 2 months •Receptor cell axons project to mitral cells in the olfactory bulb -Spherical bundles of synapses called glomeruli (single: glomerulus) -Projections from ~200 receptor cells of the same type -~50,000 mitral cells in the human olfactory bulb •Also free nerve endings -Responsible for sensations of coolness, tingling & burning from high concentrations of chemicals

Ganglion Cell Selectivity

•One ganglion cell receives input from many photoreceptors •The firing of a ganglion cell could be affected by light falling over a range of locations on the retina •This retinal area is known as the cell's receptive field (rf)

Occlusion (Interposition)

•Opaque foreground objects occlude more distant objects for areas lying along the same line of sight •Monocular, Pictorial, Visual, Ordinal •Some artists deliberately get occlusion "wrong" to create a specific effect •This can also create "impossible figures"

Centre-Surround Antagonism

•Optimal stimulus is a central spot of light - causes high activity levels well above spontaneous rate •Light all over, or no light at all cause spontaneous activity only -(There is a *slightly* larger response to more intense stimulation, but the difference is very small) •Stimulation of the surround alone causes a reduction in firing rate (below spontaneous rate) •Similar to somatosensory neurons (Lecture 3)

Orientation Channels

•Orientation aftereffect, aka tilt aftereffect -Prolonged exposure to tilted bars makes subsequently seen vertical lines appear tilted in opposite direction •To explain this, we first need to understand how orientation is normally encoded -Population coding amongst orientation selective cells (arranged in columns of cells with similar orientation preference) •Then see how neural activity is altered by prolonged stimulation -Adaptation: prolonged stimulation leads to a decrease in sensitivity & hence firing rate (cell fatigue?)

Familiarity

•Pick the matching unfamiliar face • •Tricky, but possible •Now try it with familiar faces • •EASY!

Cast Shadow

•Position of cast shadow can influence perceived depth •Depth is ambiguous - object could lie anywhere along line of sight •Assume light source is constant within a scene: Here it's overhead. Shadows lie on ground plane (whose depth is revealed through linear perspective) •Separation between object & shadow represents height of object in image •Given visual direction & height above ground plane, depth is disambiguated •Monocular, Pictorial, Visual, Metric

Methods for Measuring Infant Vision

•Preferential Looking -Gratings -Optotypes •Thumb Sucking •Visual Evoked Potentials (VEPs)

Free Fusion

•Present images side-by-side •Adjust own vergence to align 2 images -Convergence ("cross eyed") or divergent ("wall eyed") •Vergence is unnatural (just use for fun/demonstrations) •Cheap and easy

Finding your Blind Spot

•Print out this slide, or view on laptop/tablet screen •Close your left eye •While staring at the top star, move the page towards and away from you •At a specific distance, one of the numbers should disappear •Repeat while looking at the lower star •At a given distance, the line to the right should appear solid

Fusion & Diplopia

•Q. If we have 2 different images, why do we see 1 object? •A. Because of fusion -Panum's fusional area - zone around the horopter where single vision occurs (grey area in this diagram) -Combine locations of the two objects -Good metric depth -Outside this area, diplopia occurs, i.e. you see two unfused images -Diplopic images usually don't give good metric depth

Motion Cell Outputs

•Rabbit retina cells show exactly these properties (note the sub-baseline response after the motion stimulus has been extinguished) • •Also note that during stimulation, activity level drops over time

Receptive Fields & Acuity

•Receptive fields for foveal vision are smaller and more densely packed •Further out (in the periphery) they are larger & less dense •Cortical magnification: Larger area of cortex for processing foveal vision than for peripheral •Explains why foveal vision shows far greater acuity (precision)

Colour Vision with One Receptor Type

•Receptors show broad wavelength tuning -For rods, probability of absorbing ("catching") photons is highest for ~500nm (greenish), smaller probability of absorption for other ls -Hence, peak response at ~500nm, but smaller response to most ls of visible light

Reichardt detector

•Reichardt detector for leftward motion would look like this: •Motion detectors for opposite directions could be combined -This would allow us to detect motion (with the same speed) in either direction using the same 2 receptors

Why The Obsession With Gratings?

•Remember Fourier Analysis ??? -In Audition, any sound could be broken down into component sine waves having different frequencies, phases & amplitudes -In Vision, any image can be broken down into component sine waves having different: •Spatial Frequency (like sound frequency) •Phase (like phase in audition) •Orientation (no equivalent in audition) •Contrast (like sound intensity/amplitude) -Cells are selective for SF, phase and orientation -Responses are increased with increasing contrast -To some extent, our visual system does Fourier analysis

Transduction

•Retina contains light-sensitive photoreceptors -Rods •High sensitivity (night vision) -Cones •Lower sensitivity (daytime) •Rods/Cones pass electrical impulses to ganglion cells (via bipolar/amacrine/horizontal cells) •Ganglion cells have long axons that exit the eyeball via a bundle called the optic nerve •Where the optic nerve leaves the eye there are no photoreceptors - this is the blind spot

From Eye to Brain

•Retinal ganglion cell axons terminate in Lateral Geniculate Nucleus (LGN) •Crossover at the optic chiasm •Left visual field goes to right LGN & vice versa (partial decussation) •LGN projects to primary visual cortex (V1 or striate cortex) in the occipital lobe via optic radiation

Motion Perception & Eye Movements

•Retinal motion could be due to... -Object motion -Eye movements (e.g. pursuit) •How do we tell which? •Compare retinal motion with some measure of eye velocity

Photopic (day time) Colour Vision

•Rods are all "bleached out" (over-stimulated): It's down to the cones •Unlike rods, there are several different types of cone, each tuned to a different wavelength •Colour vision in daylight is good: humans can reliably discriminate at least 200 wavelengths •How many different types of cone are there? •200?

Colour Vision

•Seems almost innate •Red/green discriminated early •Blue takes longer

Olfaction Selectivity & Adaptation

•Selectivity -Receptor respond preferentially to (i.e. are "tuned" to) a particular odorant chemical (e.g. carbon chains of a given length) -This receptor may respond at a lower rate to similar chemicals e.g. ones with a slightly longer/shorter carbon chain (Wilson, 2000) - •Adaptation -Responses fall rapidly after odorant exposure -Similarly, detection becomes more difficult after adaptation -Explains why people can't smell their own body odour

The Cortex: V1 Cell Properties

•Selectivity: Orientation tuning -Cells respond to an edge or a bar with a particular preferred orientation within its RF -Reduced activity as orientation departs from the preferred -Range of orientations to which the cell fires lots is a measure of its bandwidth -Small bandwidth => sharp tuning -Large bandwidth => broad tuning -Like auditory filters/nerve fibres, olfactory receptors, etc.

Face Adaptation

•Shares many properties of adaptation in other areas of perception -Observe a particular face stimulus for a while (adaptation) -Then observe the test stimulus, which will appear transformed in some way (aftereffect) -The aftereffect is often "opposite" to the stimulus that you adapt to •Many forms (viewpoint, expression, gaze angle, sex, race, identity, etc,)

Posterior Vitreous Detachment (PVD)

•Shrinkage of vitreous humour (behind the lens), which pulls away from retina •"Floaters" •75% of people over 65yrs •Does not lead to loss of acuity but may lead to detached retina •Detached retina most prevalent among short-sighted white males

Other Kinds of "High Level" Adaptation

•Similar aftereffects can be shown for exposure to body stimuli •These effects share many common properties with aftereffects of other high level stimuli such as faces •Could these effect underlie various forms of body image disturbance?

Types of V1 Cells

•Simple Cells -Respond to an oriented stimulus in a particular location within their RF -Can be bar detectors or edge detectors •Complex Cells -Respond to an oriented stimulus anywhere within their RF •Hypercomplex Cells -As above, but prefer stimuli with an end within the RF -Or sometimes two ends -These are known as "end-stopped"

Building Cells

•Simple Cells • -Hubel & Wiesel showed how simple cells could, in principle, be "built" from the outputs of retinal ganglion cells - -Sum the inputs of ganglion cells whose RFs are appropriately arranged •Complex Cells -Connecting several simple cells -Same orientation preference -Different edge locations -Connect with an OR operation - •Hypercomplex Cells -Connect several complex cells to construct an end-stopped cell

The Aperture Problem

•Simple/Complex cells in V1 are sensitive to 1D features (edges, bars, gratings, etc.) •They respond to stimuli within a fixed receptive field (aperture) •Given no other information, we tend to see the direction perpendicular to the 1D feature, but we can't really know the actual direction •As such, motion direction of a 1D feature seen through an aperture is ambiguous - this is the APERTURE PROBLEM

Olfaction Facts

•Smell is considered a minor sense in humans, but has surprising effects •Humans can tell the sex of another person solely on the basis of the smell of their breath or hands •Synchrony of menstrual cycles in women sharing housing is believed to be based on olfactory stimuli •Pheromones play a role in sexual attraction??? •No barrier between receptors & the world (that's why people snort drugs) Newborns recognise mother partly from smell

OFF Centre Cells

•So far we have only looked at ON Centre cells -These tell us how bright an area is, and help us detect local luminance increments •OFF Centre cells do the opposite -They tell us how dark an area is, and help us detect local luminance decrements •Rather than cancelling out the effects of ON Centre cells, they compliment them •Why have 2 sets? -It's hard to go far below the spontaneous firing rate -Ensures that dark spots are detected as easily as light ones

Gratings & Spatial Frequency

•So far we've seen a lot of stripes -Technical name: Gratings •Often have a sine wave luminance profile -Sine wave gratings, sinusoids •Rather than stripes being "fat" or "thin" count how many pairs of light/dark stripes you can fit into a set space on the retina -Measured in cycles (i.e. a dark and light stripe) per degree of visual angle (cpd or deg-1) •This is the spatial frequency (SF) -Fat stripes have a low spatial frequency Thin stripes have high spatial frequency

The Plaid Fad

•Sometimes it's unclear which edges belong to which object •Plaids are a combination of two (or more) gratings at different orientations •Fashionable in the 80s/90s •With components in motion, they can look like -One coherent "checkerboard" pattern in a new direction -Two transparent layers sliding over each other •Coherence determined by similarity of -Contrast Spatial Frequency

Perceived Depth & Perceived Size

•Stare at the cross in the image on the top right for 30sec •Then stare at your hand - how large is the afterimage? •Then stare at a far surface (the wall or the white field below right) - how large is the afterimage? •Stare at the cross in the image on the top right for 30sec •Then stare at your hand - how large is the afterimage? •Then stare at a far surface (e.g. a wall) - how large is the afterimage? •Afterimage looks small projected at a short distance, but large for long distances •Why?

Stereopsis

•Stereopsis = Binocular visual cues to depth •Each eye has a unique viewpoint, and hence sees subtly different things -Euclid c.300 BC; Galen c.AD 200: It is impossible for both eyes to see the same parts of a sphere or column -Leonardo da Vinci (c. AD 1500): In real viewing, a foreground object blocks the view of different parts of the background in each eye. Paintings cannot simulate this -Wheatstone (1838): Difference in the retinal position of objects in the two eyes signals depth •Hold one finger directly in front of your nose and the other at arm's length •Close your right eye and observe the image •Repeat for left eye •Although the far finger is to the left of the near one in your left eye, it is to the right of the near finger in the right eye

Detection of Orientation Change

•Stimulus changes orientation twice per second (2Hz) •Phase change at 6Hz •Record VEPs, and note frequency •Response to phase change recorded at earliest age •Response to orientation change after about 6 weeks •Restricted to dynamic stimuli

Strabismic Amblyopia

•Strabismus - failure of the eyes to align •The 2 retinas receive different inputs •Sufferers usually favour one eye for fixation (otherwise they get diplopia) •Abnormal development of monocular & binocular cells for the non-favoured eye, and poor visual function •Few cells that are selective for high spatial frequencies •This is "amblyopia" (trans: "blunted vision") aka "lazy eye" •Early eye-alignment operation can help, but after the critical period, it is too late: correct development never occurs

Face Perception or Image Perception ?

•Studies that use the same image (for learning & recall phases in memory tasks, or for the matching stimuli in perceptual experiments) may not reveal anything about the details of processing faces per se •Humans are good at remembering/matching images (of faces or of any other objects) •In real life we never see the same image twice (different lighting/viewpoint/expression, etc.) •Consider the following "police identity parade" style examples...

Somatosensory Transduction

•Tactile receptors (mechanoreceptors) -Meissner's Corpuscles -Merkel's Disks -Ruffini's Corpuscles -Pacinian Corpuscles •Selectivity -Superficial receptors (Meissner/Merkel) respond best to light touch -Deep receptors (Pacinian/Ruffini) respond best to pressure and stretch

The Critical/Sensitive Period

•Visual deprivation has no effect on adult animals (or humans) •Deprivation is most effective if it's during an early period during which development is taking place •If deprivation ends before the end of this period, normal development resumes •This is known as the "critical period", or the "sensitive period" •For cats this period is short (a few months), longer for monkeys (>1yr) and for humans even longer (~6yrs?) •But note that there may be different critical periods for different aspects of perception

Visually Evoked Potentials (VEPs)

•Visual patterns cause changes in electrical activity in the brain -Infer that if there is activity, then infant can see the image that caused it •External electrodes measure brain activity through the scalp -No response required •Need to detect the activity caused by the pattern ("signal") in presence of background neural activity ("noise") -Repeat many times & average -Signal should be the same for each presentation, but the noise should be random and will eventually cancel out

Some Gustation Facts

•Vital for detecting nutritious foods and to avoid poisoning •Facial expression of disgust -Readiness to eject foul tasting substances? -Dis + Gust = Not + Tasty! •Conditioned Taste Aversion -CSTaste + USIllness Þ CRAvoidance -One-trial learning Can last a lifetime

Depth Perception The Story So Far...

•We have seen how the visual system... -Recognises edges -Represents information about different •Orientations •Scales (spatial frequencies) -Perceives colour -Encodes motion •A (moving) 2-D representation of a 3-D world •Yet depth perception is crucial for even very simple tasks •HOW ??? -What information is available from the visual scene?

A Two Receptor System

•What if we had 2 cone types? -Colour represented by the relative activation of the 2 cone channels (call them "M" and "L") -As l changes, pattern of relative activation changes •Short ls: more activity in M cones than in L cones •Medium ls: equal activity in each cone type •Long ls: L activity > M activity -As intensity changes, activity changes equally in both channels: hence the relative activation remains the same •Bright medium ls produce equal high activity in each cone type •Dim medium l s produce equal low activity in each cone type Allows us to tell a lchange from an intensity change

Wavelength (l) and Colour

•What is wavelength (l)? -Light is (kind of) a wave -l is the distance between the crests (nm) - •What is intensity? -Intensity is the wave's "height" -Approximates to brightness - •Different pure, single l appear to us as different colours -l is an objective property of the stimulus •Short ls look purpleish/blueish; •Medium ls look greenish •Long ls look reddish -Colour is a subjective property of the percept •i.e. the experience you have when you see particular l (or combination of ls) it exists only in your head

Spatial frequency tuning

a cell preferentially responds to stimuli in a particularly spatial frequency range

Cochlea

a coiled, bony, fluid-filled tube in the inner ear through which sound waves trigger nerve impulses

Acuity

(n.) sharpness (particularly of the mind or senses)

Perception: Our link to reality

- "out there" is only physics - "in here" is only psychology Physical stimuli are "transduced" into nerve impulses by our sense organs We experience these as a reconstruction or representation of the world: sounds, shapes, colours, smells, heat etc.

Single Cell Recording

- Anaesthetised or awake - Microstimulation (awake) - High spatial and temporal resolution - Difficult to get the big picture

Optical Imaging

- Blood flow dependent changes - Small area of cortical surface - Slow response

Fourier Analysis

- Definition: to decompose a complex sound into its frequency (sine-wave) components - This 'decomposition' is usually displayed visually in a spectrogram - a graphical representation of changes in the frequency content of a signal over time - Time is plotted horizontally, frequency is plotted vertically, and amplitude is represented by the darkness of the plot

Vestibular Transduction

- Each semicircular canal contains a bundle of hair cells called a cupula projecting across the canal - The utricle and saccule each contain a patch of hair cells (macula) covered in a gelatinous carpet (otolithic membrane) - Head acceleration or static tilts deflects the hair cells away from their resting position, causing activity in sensory nerves

Doctrine of Specific Nerve Energies

- Each sense projects to a different cortical area - The nature of a sensation depends on which sensory fibers are stimulated, not on how fibers are stimulated

Forensic Psychology

- Eyewitness testimony - Weapons focus - Facial identification - Police Identity Parades - Other Race Effect

Bottom up and Top Down

- It is not a dichotomy - Both undeniably exist - There must be a bottom up, otherwise how would information get in? - Patients in a coma, or anaesthetised animals show substantial activation through the visual pathway - Top down influences are clear in the dolphin example, and many, many others - Forward, lateral and backward connections in the visual pathway demonstrate that information can flow in all directions

Tactile receptors

- Meissner's Corpuscles - Merkel's Disks - Ruffini's Corpuscles - Pacinian Corpuscles

Psychophysics: Measuring Sensory Magnitude

- More intense stimulus = higher magnitude of sensation Measure with Magnitude Estimation technique - Present a "modulus" stimulus and call it "10" = Participants rate various stimuli differing in intensity Compressive non-linear functions (except for electric shock!) - i.e. if you double the intensity, the sensation is less than double (e.g. approx 1.5 times the size of this graph)

Psychophysical linking hypothesis

A linking proposition positing a specific causal link between neural activity in the brain and perceptual experience

Ion channel

a complex of protein molecules in a cell membrane that form a pore through which ions can pass

Preferential Looking Discrimination

-2 gratings -Baby "habituates" when a stimulus is presented repeatedly -Put repeated stimuli next to novel stimuli (instead of blank patch) -Baby should prefer to look at novel stim -No preference => baby can't discriminate the stimuli

•Principle of Univariance

-A receptor's activity is related to the number of photons it catches, not to the type (l) of photon -Same response to 450 (blueish) or to 650nm (orangeish) light at 160cd/m2 Response to 550 nm (green) light can A receptor's activity is related to the number of photons it catches, not to the type (l) of photon Same response to 450 (blueish) or to 650nm (orangeish) light at 160cd/m2 Response to 550 nm (green) light can be the same also if intensity is reduced to 80cd/m2 One lone receptor can only tell light from dark Any l can look like any other l, given the right intensity Hence bad colour vision at night (rods only)

•Herman Grid

-Again, consider the responses of an ON centre retinal ganglion cells at intersections (darker areas) or on the white bars (lighter) -Stimulation of the 2 central excitatory regions is identical • -Cell at the intersection gets more light on the surround, i.e. more inhibition compared to the one on the white bar

Preferential Looking Detection

-Grating vs. blank patch -Baby prefers looking at grating pattern vs. blank -No preference => baby can't detect the stimulus -Vary spatial frequency to establish "peak contrast" resolution/acuity limit -Vary contrast to establish entire CSF

•Why are grey patches more pronounced in the periphery?

-In the fovea, receptive fields tend to be small and densely packed -As we move to the periphery, RFs tend to be larger •This is why we have to move our eyes to get better acuity for the object of interest -Herman grid illusion works best when excitatory portions of RFs fit into the intersections, with inhibitory surrounds overlapping the darker squares (as shown in the diagram) -Where RFs are too small (or intersections are too large) at that eccentricity then there will be no grey patches

Rods

-Only one type -None in central fovea -High sensitivity -Night vision -Scotopic

There is an argument that the processing of faces is not special

-Prosopagnosics often show impaired recognition ability for non-face objects within a category (e.g., birds, cars, etc). -After training to recognize non-face objects (e.g. "Greebles"), normal subjects •show face-recognition-like performance (e.g., inversion effect, composite effect) •brain activity shifts from object area to FFA •Perhaps expertise is what's special? -We are all face experts -The same (face) effects hold for anything you're an expert at processing

Cones

-Several types, each tuned to a different ls -Mostly in fovea -Lower sensitivity -Day vision Photopic

Modal completion

-Surfaces completing in front of another even though the border is not visible -Completed surface is seen (illusory surface) -In real life, much less common than amodal completion

primary olfactory cortex

-located within temporal lobe -provides conscious awareness of smells

Inflow vs. Outflow Theory example 2

. Externally generated eye movements with an isolated AI -Poke yourself in the eye, with an AI, in the dark •Inflow predicts motion (No retinal motion, but there is a muscle movement signal) •Outflow predicts no motion (No retinal motion, no efference copy command) •No motion perceived (Outflow correct)

Inflow vs. Outflow Theory example 3

. Externally generated eye movements with non-stabilised stimuli -Poke yourself in the eye in daylight (no AI). Image moves on retina. •Inflow predicts no motion (Retinal motion & eye muscle movement signal are = & opposite) •Outflow predicts motion (Retinal motion, but no efference copy command) •Motion IS perceived (Outflow correct)

Three observations hint at the complexity of the brain processes involved in perception:

1. A large proportion of the brain's highly developed structure, the cerebral cortex, is devoted entirely to perception. 2. Computer scientists have never been able to create a replica model of the brain 3. Result of brain damage and lesion studies are less than straight forward

The Rubber Hand Illusion is reduced when presenting:

1. Asynchronous Touch 2. Incongruent Orientations 3. Non-body Objects

For simple sine waves:

1. Place Theory • Explains pitch for sine waves very well BUT not how we discriminate two sine waves at high frequencies • Can't explain missing fundamental 2. Timing (Rate) Theory • Explains pitch for low/mid frequencies very well

For complex sound waves:

1. Temporal Theory • Explains low frequencies very well - frequencies up to 4kHz explained by volley principle 2. Pattern Recognition Theory • Explains pitch for sine waves similar to place theory • Can explain the 'missing fundamental' effect

Image Based vs. Symbolic Object Representation

A lively debate! Image Based • Based on neural image to compute representation • Lower/earlier levels Symbolic representations • Symbols manipulated to build representations (e.g., geons) • Highest levels The neurophysiological evidence: = serial processing scheme - both view dependent and view - independent representations

Vision in Old Age

1.Presbyopia •Lens loses flexibility -Decrease in accommodation (complete loss by ~55yrs) •Corrective lenses required depends on fixed state of the lens -May need glasses for distance/reading -May need bifocals or varifocals (aka progressive lenses) - 2. Yellowing •More blue light absorbed •Less able to tell dark blue from black 3. Posterior Vitreous Detachment (PVD) •Shrinkage of vitreous humour (behind the lens), which pulls away from retina •"Floaters" •75% of people over 65yrs •Does not lead to loss of acuity but may lead to detached retina •Detached retina most prevalent among short-sighted white males 4. Age Related Macular Degeneration (AMD) •UV light absorbed by macula which can damage retina •Yellow deposits ("drusen") in macula •Loss of central vision •Major cause of blindness in over 50s •Dry AMD and Wet AMD •No treatment or cure •Prevention only -Wear sunglasses with UV filters -stop smoking -eat brightly coloured vegetables, rich in antioxidants (???)

Why do this?

2 reasons: •It tells you where the changes are in the image -Exaggerates edges -Edges are crucial, as they define object boundaries •Allows us to compensate for intensity of the light source -Sensitivity to contrast between light and dark, not so much to overall brightness -Higher contrast - more cell activity

Solving the Aperture Problem

2 ways that the human visual system can solve the aperture problem: •Identify 2D features at the edge of object -Intrinsic Terminators - •Integrate information across 1D features at different orientations -Intersection of Constraints

Probe Stimulus

220 Hz tone varying levels of pressure Varying pressure above and below atmospheric pressure causes tympanic membrane and ossicular chain to stiffen

two-alternative forced choice

2AFC

Double opponent cell

A cell type, found in the visual cortex, in which one region is excited by one cone type, combination of cones, or color and inhibited by the opponent cones or color (e.g., R+/G-). Another adjacent region would be inhibited by the first input and excited by the second (thus, in this example, R-/G+).

Orientation column

A column in the visual cortex that contains neurons with the same orientation preference.

Binocular disparity (stereopsis)

A cue for depth perception that depends on the fact that the distance between the eyes provides two slightly disparate views of the world that, when combined, give us a perception of depth.

Stereoscope

A device for presenting one image to one eye and another image to the other eye

What is sound?

A disturbance that travels through a medium as a longitudinal wave

contrast sensitivity function (CSF)

A function describing how the sensitivity to contrast (defined as the reciprocal of the contrast threshold) depends on the spatial frequency (size) of the stimulus.

Cupula

A gelatin-like structure containing a tuft of hairlike sensory receptor cells in the semicircular canals.

Emmert's law

A law stating that the size of an afterimage depends on the distance of the surface against which the afterimage is viewed. The farther away the surface, the larger the afterimage appears.

reichardt detector

A neural circuit that results in neurons firing to movement in one direction. Excitation and inhibition are arranged so that movement in one direction creates inhibition that reduces or eliminates neural responding, whereas movement in the opposite direction creates excitation that enhances neural responding.

random dot stereogram

A pair of stereoscopic images made up of random dots. When one section of this pattern is shifted slightly in one direction, the resulting disparity causes the shifted section to appear above or below the rest of the pattern when the patterns are viewed in a stereoscope.

parallax barrier

A parallax barrier is a device placed in front of an image source, such as a liquid crystal display, to allow it to show a stereoscopic or multiscopic image without the need for the viewer to wear 3D glasses.

Anomalous trichromat

A person who needs to mix a minimum of three wavelengths to match any other wavelength in the spectrum but mixes these wavelengths in different proportions from a trichromat.

Thatcher illusion

A phenomenon in which people have difficulty noticing local feature changes (e.g., upside down eyes or mouth) in an upside down face.

Loudness

A physical response to the intensity of sound, modified by physical factors

Prism

A piece of glass that seperates white light into colors of the spectrum.

Microstimulation

A procedure in which a small electrode is inserted into the cortex and an electrical current passed through the electrode activates neurons near the tip of the electrode. This procedure has been used to determine how activating specific groups of neurons affects perception.

Selective rearing

A procedure in which animals are reared in special environments. An example of selective rearing is the experiment in which kittens were reared in an environment of vertical stripes to determine the effect on orientation selectivity of cortical neurons.

Lateral antagonism

A process in the retina that occurs when neural activity in a cell opposes activity in surrounding cells.

Method of Constant Stimuli (MoCS)

A psychophysical method in which a number of stimuli with different intensities are presented repeatedly in a random order.

vector

A quantity that has magnitude and direction

Photons

A quantum, or discrete quantity, of light energy that behaves as if it were a particle.

Cone of confusion

A region of positions in space where all sounds produce the same time and level (intensity) differences (ITDs and ILDs).

Medial Superior Olive

A relay station in the brain stem where inputs from both ears contribute to detection of the interaural time difference.

Monosodium Glutamate

A salt that interacts with other ingredients to enhance salty and sour tastes MSG

Gestalt Laws of Organization

A series of principles that describe how we organize bits and pieces of information into meaningful wholes

Sensitivity

Ability to recognize and appreciate the personal characteristics of others

simultaneous brightness contrast illusion

Abstract Simultaneous brightness contrast and simultaneous color contrast are classical illusions that demonstrate how our perception can be altered by spatial context; a central gray region appears to have brightness and color that are complementary to those of a surrounding region.

misapplied constancy scaling

According to Misapplied Size Constancy Scaling (Gregory, 1997) the illusion is due to the perceptual system misperceiving the lines as being different distances from the observer, which in turn, affect their relative perceived sizes, due to the bounding arrowheads being interpreted as conveying three- dimensional

Semantic Consistency Potter & Davenport (2004)

Affects object perception • 80ms: objects and backgrounds were reported more accurately when they were semantically consistent with each other than when they were inconsistent

2. View-dependent theory

Alignment - surface markings and junctions • Shape space - multidimensional metric space representing variations in object shape • Recognition - compare a novel 2D view to stored views of known objects

Electromagnetic spectrum

All of the frequencies or wavelengths of electromagnetic radiation

waterfall illusion

An aftereffect of movement that occurs after viewing a stimulus moving in one direction, such as a waterfall. Viewing the waterfall makes other objects appear to move in the opposite direction.

Square wave

An almost instantaneous rise and decay of voltage or current in a periodic pattern with time and with a constant peak value.

Hollistic processing

An alternative account suggests holistic processing is a fast, early grouping process that first serves to distinguish faces from other competing objects. From this perspective, holistic processing is a quick initial response to the first-order information present in every face

Cortical receiving area

An area of the cortex where afferent (incoming) fibers from a sense organ terminate; also known as primary sensory cortex.

Tonotopic organisation

An arrangement in which neurons that respond to different frequencies are organised anatomically in order of frequency

Visual processing is hierarchical

Early: basic features - lines, angels, orientation Pathways: "what" (ventral) and "where" (dorsal) brain - processes more complex aspects e.g., visual form

Inflow vs. Outflow Theory example 4

Attempt to move a paralysed eye -Curare or wedge •Inflow predicts no motion (No retinal motion & no muscle movement) • •Outflow predicts motion (No retinal motion, but there is an efference copy command) • •Motion IS perceived (Outflow correct)

Low pass filter

Attenuates high frequency energy but passes low frequency energy

Auditory Nerve Filters

Auditory nerve cells filter on the basis of frequency • They let the neural signal through for frequencies that they are tuned to, and filter it out for others • "Band-pass filter"

Ascending Auditory Pathway

Auditory nerve fibres terminate in the cochlear nucleus (one on each side). ª Binaural neurons found in superior olive, taking inputs from both ears ª Thalamic relay is called the medial geniculate nucleus

Pitch Perception of Sine Waves: Timing Theory (Rate Coding)

Auditory nerve responses are phase-locked to a sound-wave's frequency below 4-5kHz • Response rate of neural impulses carries information about sound frequency • Assumes the listener discriminates the pitch of sine waves by means of differences in response rate or time intervals between neural firings • Evidence suggests - Timing theory and rate coding important for pitch of low/mid-range frequency sine waves - For high frequencies, place theory (poorly) conveys pitch of sine waves

Synesthetic congruency

Auditory pitch: Vertical spatial location (elevation) Brightness & lightness Size Angularity of shape Direction of motion Spatial frequency Elevation of tactile stimuli Size of haptically experienced objects • Tastes: Angularity of visual stimuli Pitch of auditory stimuli Spence & Delroy, 2013 • Loudness: Brightness Etc • Odours: Colour (hue, brightness, saturation) Pitch Tactile softness

Pitch Perception of Sine Waves: Place Theory (Place Coding)

Auditory system is an approximate Fourier Analyser - Resolves complex sounds into their component sine waves through a bank of frequency-tuned filters - Frequencies of components are given by the location of the most active fibres in the basilar membrane • Place theory predicts that pitch discrimination for pure tones should depend on the bandwidth of auditory filters • Precise place of the vibrating segment of the basilar membrane would signal the existence of a component at the natural frequency of that location • Frequency-to-place conversion Critical bandwidths provide a good psychophysical method of estimating filter properties • Critical bandwidths increase with frequency • Frequency discrimination is very good at low frequencies, much worse at high frequencies • But frequency discrimination performance is not a constant proportion of bandwidth, as it should be according to place theory

lateral

Away from the midline of the body

Somatosensory Hierarchy

Axons follow two routes to the brain - The spinothalamic pathway carries relatively slow temperature signals from free nerve endings - The lemniscal pathway carries relatively fast signals from mechanoreceptors Both pathways have branching circuits in the spinal cord that mediate reflex responses

Clinical Psychology

Eating disorders - Body image distortion - a perceptual component? Inability to recognise facial emotion in - psychopaths - people with depression, autism, schizophrenia

Hierarchical Processing: Bottom Up vs Top Down

Bottom up - Flow of information from sensory receptors towards "higher" cortical areas with increasing levels of complexity Top Down - Prior knowledge influences what is perceived

Bottom-up versus top-down models

Bottom-up models propose that body self-perception is driven by the detection of statistical correlations between incoming multisensory signals (Armel & Ramachandran, 2003) • Top-down models propose that the processing of incoming multisensory signals is combined with stored information about what the body is typically like (e.g. Tsakiris, 2010, Carruthers, 2008, Carruthers, Gao, Zopf, Wilcox and Robbins, 2017) • Top-down models more supported by RHI findings

The Kanizsa Triangle

Brain tries to see common shapes

Adaptability

Capable of being modified to suit different conditions or a different purpose

Simple cells

Cells in V1 that respond to line, or gradient, oriented in particular direction

Complex cells

Cells in V2 that give best response to moving lines of particular orientation

Ampula

Enlargement at the base of the semicircular canals, contains the cupula and the crista

Deuteranomaly

Color blindness due to a partial lack of green cones.

Protanomaly

Color blindness due to a partial lack of red cones.

Pitch Perception of Complex Tones

Contain a series of harmonic frequency components spaced at intervals equal to the frequency or repetition rate of the fundamental • The pitch heard in a complex tone is usually determined by the fundamental frequency Contain a series of harmonic frequency components spaced at intervals equal to the frequency or repetition rate of the fundamental • The pitch heard in a complex tone is usually determined by the fundamental frequency • A phenomenon known as the "missing fundamental" presents a basic problem for place theory as an explanation of pitch in complex tones

Ocular dominance columns

Cortical columns consisting of neurons that receive signals from the left eye only or the right eye only

atmospheric perspective

Creating the illusion of depth of space by fading colors and eliminating detail in objects that are further away.

cyclopean vision

Cyclopean image is named after the mythical being, Cyclops, a creature possessing one single eye. The single refers to the way stereo sighted viewers perceive the center of their fused visual field as lying between the two physical eyes, as if seen by a cyclopean eye.

Neuropsychological Evidence

Damage to early pathway: blindness • Further along: inability to process colour, motion etc. • Even further along: specific object recognition deficits, intact basic visual features

Disordered Object Perception: Agnosia

Damage to extra-striate cortex (next to primary visual cortex) • Complete visual fields • Normal colour, depth and movement 2 types - Apperceptive - Associative

Phase

Defines a particular point on a waveform. Measured in degrees and corresponds to changes to the perceived quality of the sound

pictorial depth cue

a cue to distance or depth used by artists to depict 3-D depth in 2-D pictures

Discrimination: Two Point Acuity

Differences in perceived touch location - Use Yes-No or 2AFC procedure - A pair of callipers is placed on the skin surface - Subject reports whether they feel 1 or 2 points - Callipers adjusted until subject can just report the presence of a pair of points reliably (discrimination threshold of JND) Variation in acuity with body location mirrors cortical magnification - JNDs are smallest for mouths and fingers, and largest for neck and back - Receptive fields small for mouth/fingers, large for neck/back

Staining techniques

Direct examination of sample completed in the lab

Additive mixture

Direct mixtures of different wavelengths of light in which all of the wavelengths reach the retina and are added together.

Pros & Cons of Frontal Eyes

Disadvantage of having frontally placed eyes is that it reduces the total visual field But for objects in the binocular field, it gives us... Binocular Summation Two "chances" to see the object Lower thresholds (detection/discrimination) Depth Perception Two separate viewpoints Allows us to extract depth information

Frontal Plane

Divides the body into front and back portions.

frontal plane

Divides the body into front and back portions.

Pitch Perception: Pattern Recognition Theory

Goldstein (1973) - Auditory system resolves individual sine wave components and analyses frequencies using place code - Then tries to find a series of harmonically related frequencies that fits the resolved components - Pitch is determined by the fundamental of the best-fitting harmonic series - Can explain missing fundamental effect, since the pitch of the fundamental is defined by the harmonics present in the stimulus, even when the fundamental is not present

Gestalt Laws

Ground Figure, Connectivity, Proximity, Similarity, Closure

Unresolved harmonics

Harmonics of a complex tone that can't be distinguished from one another because they are not indicated by separate peaks in the basilar membrane vibration. The higher harmonics of a tone are most likely to be unresolved.

Cone monochromat

Have only one cone type; truly color-blind

Amplitude

Height of a wave

Henning's taste Tetrahedron

Henning's taste tetrahedron an arrangement to represent four putative primary tastes: sweet, salty, sour, and bitter.

Hz

Hertz

Wavelength

Horizontal distance between the crests or between the troughs of two adjacent waves

Theories of Pitch Perception

How do we perceive pitch? Four theories 1. Place theory (Helmholtz, 1877) 2. Timing (Rate) theory 3. Temporal Theory 4. Pattern Recognition theory Has to explain 1. How we perceive sine waves 2. How we perceive complex tones

Motion Detectors

How would we design a unit that could signal motion in a particular direction? •"Reichardt Detector" •Neighbouring receptors "delay and compare" -One receptor's output is delayed by some fixed time -If spikes reach "AND" unit simultaneously, then it fires •No firing for motion in "null direction" (opposite direction) •Would need many units with many delays & separations to represent all speeds

Face recognition

Identify faces in images Temporal lobe

The Case of the Missing Fundamental!

If the fundamental frequency of a complex tone is removed, its pitch is still heard at a frequency that corresponds to the fundamental • ...even when the fundamental frequency component is removed! • Place theory cannot account for this

wagon wheel effect

Illusion that a spoked wheel is moving backward rather than forward; can occur in film or under flickering UV lights.

Kitten Carousel - Held and Hein

Kittens because they are born blind - Kitten A - Roam Free (active), Kitten B - in basket controlled by Kitten A (passive) - Kitten A - received feedback, Kitten B - no feedback - Kitten A - normal vision, Kitten B, poor depth perception (almost none) Tests: - Visually guided paw placement - kitten held with head and forelegs free to the edge of the table - Avoidance of visual cliff - Kitten place on central 'bridge' (clear ground to show edge of cliff) - Blink to approaching object - Experimenter moving finger towards kittens eyes

Light Intensity

Light intensity = intensity of electromagnetic wave? But not all wavelengths are visible - need a scale that takes visibility into account Luminance (candelas/m2 or cd m-2) Vision works in a wide range of different luminances Factor of 10,000,000 difference between star- & sunlight Objects reflect different percentages of the incident light E.g. white paper ~75%, black paper ~5% (i.e. 15:1 ratio)

Focusing

Light rays from a single point spread in all directions Focussing is recombining rays from various directions to form a single point on the imaging surface In the eye, this job falls to the cornea and lens Cornea is curved - light refracts a constant amount Cornea has greater refractive power Lens refracts light by a variable amount Accommodation: lens can be stretched to allow focussing of far objects

Ruffini's Corpuscles

Long-term pressure and heat receptors

Loudness Perception

Loudness is the perceptual attribute that corresponds to intensity • Different intensities can have equal loudness due to frequency • In loudness matching, adjust the intensity of a comparison or "probe" tone until it matches the loudness of a fixed standard pure tone - method of adjustment (Moore, 1997) - Plot equal-loudness contours - Sensitivity is poor at low freq - At mid-intensity, low-freq sounds lack loudness compared to high-freqs - This is why some stereos have a "bass boost" - As intensity increases, the curves flatten out

Candelas per square meter

Luminance is measured by

Apperceptive Agnosia

Maps on to Stage 2 • Deficient shape representation • Unable to copy or match

Associative Agnosia

Maps on to Stage 3 • Deficient object representation

Symbolic Segmentation

Marr's Primal Sketch: computational modelling • List of local features or primitives (edges etc) • Each primitive had certain properties • Grouping based on similarities on: • AVERAGE LOCAL INTENSITY • AVERAGE SIZE • LOCAL DENSITY • LOCAL ORIENTATION • ETC.

Is the Ear a Fourier Analyser ?

Maybe... ª Auditory filters separate frequencies into different 'channels' ª Responds to amplitude within each channel ª Can encode phase information ª But not quite... ª Due to non-linearities between the input and the output ª 2 tones should result in two peaks, but often 3 peaks merge ª Outer hair cells amplify small intensities

Image-based Segmentation

Mechanism which helps visual system parse image into basic meaningful regions Texture Based: - Proximity: spacing creates visual texture differences between regions - Similarity: size, shape, colour also Motion-and-depth-based segmentation - Common motion (fate) or stereoscopic disparity used

A Two Receptor System Metamers

Metamers: 2 different physical stimulus configurations that appear identical •For a 1- receptor system (e.g. rods at night) all ls can be metamers for each other (at the right intensities) •For a 2-receptor system... •For mid l light, both channels give the same response (see top fig.) •Both channels also give same response to mix of short + long l at the right intensities (see bottom fig.) •These are metamers for each other -In fact, almost any two ls of light, when mixed in the correct intensities could match any given l

aerial perspective

Monocular cue to distance and depth based on the fact that more distant objects are likely to appear hazy and blurred.

LGN Properties

Mostly like ganglion cell properties Centre-surround antagonism 6 layers Each is retinotopically organised Neighbouring cells have retinal RFs next to each other All cells are monocular Both eyes have inputs to LGN, but each eye goes to separate layers Layers 1, 4 & 6 from contralateral eye Layers 2, 3 & 5 from ipsilateral eye Only one visual hemifield (contra) •Magnocellular vs Parvocellular -Large/Small RFs (Low/High resolution) -Fast/Slow response -High/Low sensitivity -Process motion/R-G colour •Koniocellular -Between M/P layers B/Y colour???

transparent motion

Motion transparency occurs when multiple objects move over the same region of space. Examples of motion transparency are when an animal moves through tall

Inflow vs. Outflow Theory example 1

Move eyes around with an afterimage -Afterimages (AIs) are fixed on the retina •Inflow predicts motion (No retinal motion, but there is a muscle movement signal) •Outflow predicts motion (No retinal motion, but there is an efference copy command) •Motion IS perceived (Both theories correct) Like perfect pursuit of a moving object, or chasing a "floater"

Overall Summary

Multisensory processing is integral to perception • Neural mechanisms involve a network of brain areas including feedforward and feedback connections • Several factors influence the strength of multisensory interactions including the effectiveness of unisensory stimuli, as well as temporal synchrony, spatial correspondence and synesthetic congruency between multisensory signals • Synaesthesia is an unusual form of integration that is consistent over time, involuntary, and follows similar patterns to cross-modal mappings in non-synaesthetes • Multisensory perception is integral to body perception and can be studied with the rubber hand illusion paradigm

Image-based Contour Integration

Need to know where borders end • Contours describe boundaries of objects or parts • Earliest levels of visual analysis • Local edge responses are bound together = representation of extended contours • Silhouettes sufficient for recognition

Auditory Nerve and Characteristic Frequencies

Nerve cells send signals along the auditory nerve toward the brain ª Auditory nerve fibres respond best to particular "Characteristic frequencies" ª These correspond to their hair cell's position on the basilar membrane ª Note: fibres still fire a little to frequencies close to their characteristic ª "Frequency-tuned auditory filters"

Feed forward

Neural preparation for anticipated movement, based on instruction, experience, and the ability to predict movement requirements and/or outcome.

Off centre cells

ON center/OFF surround cell: Flashing small bright spot in the center subregion increases the cell's response. ... An OFF-center/ON-surround ganglion cell has the opposite arrangement. It gets inhibition from a small spot of light in the center, and excitation from an annulus in the surround.

1. View-independent Theories

Objects are represented in terms of a structural description of their parts, independent of extrinsic factors a) Marr & Nishihara's (1978) • Base descriptor for all object parts = a 3D generalised cone • Hierarchical • Axis is crucial b) Biederman's (1987) geons Two-dimensional Limited set of 36 geometric shapes (geons)

Analog representation

Objects can take on any continuous value.

Contrast

Objects reflect different percentages of the incident light E.g. white paper ~75%, black paper ~5% (i.e. 15:1 ratio) Relative luminance is constant regardless of absolute luminance Call it Contrast (C), defined as: ...where Lmax & Lmin are the largest & smallest luminance values respectively 0-1, or sometimes a %age (0-100) When Lmax = Lmin, contrast is ZERO (i.e. there's nothing there to see!)

• Some types of synaesthesia are more common than others:

Often involves abstract forms (numbers, alphabet, dates) and colour • Less common: Colours from pain, internal sensations (e.g., hunger), touch, smells, tastes Non-colour experiences such as synaesthetic smells, tastes, touch

attached shadow

On the object itself, cannot be seen independent of the object

Sine wave

One in which amplitude varies in proportion to the sine function of an angle.

Psychometric function

a curve that relates a measure of perceptual experience to the intensity of a physical stimulus

Primary Visual Cortex (V1)

Optic radiations carry neural signal from LGN to V1 •V1 is retinotopic -Neighbouring cells have retinal RFs next to each other •Cortical magnification -More cortex devoted to fovea •Selectivity for orientation (A) -Many "channels" selective to different angles •Selectivity for eye-of-origin (B) -"Ocular dominance" ranges 1-7 -1 & 7 purely monocular (1,7) -Others binocular (2, 3, 4, 5, 6) -Binocular neurons play a role in estimating depth - see Depth Perception Lecture

Colour deficiency

People with this condition (sometimes incorrectly called colour blindness) see fewer colours than people with normal colour vision.

Synaesthesia

Perception of a specific stimulus induces a concurrent and distinct experience in a separate modality, or within the same modality Consistent over time Prevalence: 0.05-4% Gender bias: ~2-6 females to every 1 male High prevalence among biological relatives Not a disorder!

lenticular

Pertaining to the crystalline lens

Pitch Perception: Temporal Theory

Phase locking for tones up to 1kHz for individual fibres • Volley principle important for tones up to 4kHz • For higher frequencies, two harmonics should fit into the wider bandwidths of single auditory filters • These "unresolved harmonics" can produce "beats" as their waveforms overlap The frequency of beats from unresolved harmonics is the same as the fundamental • This is known as "residue pitch" • If nerve firing becomes phase locked to this frequency, perhaps temporal theory can account for the missing fundamental? • BUT when lower (resolved) harmonics and higher (unresolved) harmonics specify different fundamentals, humans rely more on the resolved harmonics (Plomp, 1967)

Summary Mechanisms of multisensory processing

Several key areas of the brain contain neurons that respond to sensory inputs from two or more modalities (e.g., superior colliculus, parietal and prefrontal cortex) • The standard feedforward account of multisensory processing needs revisions to include direct connections between sensory areas, and more extensive feedback connections • Important factors for multisensory processing include: • Effectiveness of unisensory stimuli (Inverse Effectiveness) • Temporal Synchrony • Spatial Correspondence • Synesthetic congruency

Adaptation

Prolonged stimulation results in a decrease in the rate of firing (physiology) Various perceptual consequences - Increased detection thresholds for same/similar stimuli - Reduction of perceived intensity for similar suprathreshold stimuli - Perceived properties of other similar stimuli can appear biased e.g. the motion aftereffect that you saw in the first hour

Terminators or Intersection of Constraints?

Psychophysics •45deg line segments move •When lines appear independent... -Seen as independent lines moving vertically (terminator motion)... •When occlusion is seen (i.e. terminators become "extrinsic")... -Seen as diamond moving behind 3 columns (intersection of constraints) •Lorenceau Diamond Physiology Terminators •End-stopped neurons process terminator motion as early as V1 •Hypercomplex cells • Intersection of Constraints •V1 simple/complex cells tend to respond to component motion -They suffer from the aperture problem •MT cells tend to respond to pattern motion regardless of component direction -They have solved the aperture problem!

Factors influencing the Rubber Hand Illusion

RHI allows teasing apart body perception factors by creating multisensory conflicts: body vision and proprioception, viewed and felt touch The RHI tends to work when presenting: 1. An artificial hand-shaped object in a plausible orientation and synchronous multisensory signals 2. It does not seem to matter that the hand does not look exactly like one's own hand and that the hands are in different locations

Terminators

RNA sequences that provide the signal to RNA polymerase for stopping transcription

Selectivity: Cortical Receptive Fields

Receptive Fields - Each cortical cell responds to stimulation in a small area of the body surface - The area wherein touch affects activity in a given cell is known as its "receptive field" Centre-Surround Antagonism (aka lateral inhibition) - Cell activity is increased by stimulation in the centre (A) - Firing rate is decreased by stimulation in the surround (B) - Stimulation in both areas hardly results in any change at all Amplifies responses to differences in stimulation within the RF

Outer hair cells

Receptor Cells that show convergent connectivity, for loudness discrimination

Golgi Tendon Organs

Receptors sensitive to change in tension of the muscle and the rate of that change

Joint receptors

Receptors surrounding a joint that respond to pressure, acceleration, and deceleration of the joint.

familiar size

a depth cue based on knowledge of the typical size of objects like humans or pennies

Koniocellular

Referring to cells in the koniocellular layer of the lateral geniculate nucleus of the thalamus. Konio from the Greek for "dust" referring to the appearance of the cells.

persistence of vision

Refers to the way our eyes retain images for a split second longer than they actually appear, making a series of quick flashes appear as one continuous picture.

Optic disc

Region at the back of the eye where the optic nerve meets the retina. It is the blind spot of the eye because it contains only nerve fibers, no rods or cones, and is thus insensitive to light.

multisensory convergence zones

Regions in the brain that receive input from multiple unimodal areas processing different sensory modalities.

Top down

Research has shown that young children cannot identify the amorous couple in this picture - Children see 9 dolphins

On centre cells

Respond to lights shone in central region of their receptive fields w/ on firing & to lights shone in periphery of RF w/ inhibition by "off" firing when light is turned off

From Eye to Brain

Retinal ganglion cell axons terminate in Lateral Geniculate Nucleus (LGN) Crossover at the optic chiasm Left visual field goes to right LGN & vice versa (partial decussation) LGN projects to primary visual cortex (V1 or striate cortex) in the occipital lobe via optic radiations

Photoreceptors

Rods Cones

geons (geometric ions)

Simple geometric figures, such as cubes, cylinders, and pyramids, that can be combined to create all other shapes. An early (and crucial) step in some models of object recognition is determining which geons are present.

SIRDS

SIRDS stands for Single Image Random Dot Stereogram. It's a type of optical illusion that exploits the way our brains work to figure out spatial information from stereographic vision. Cognitive psychologists have been interested in how we see and assimilate information about our environment.

pursuit

Saccades are rapid eye jumps, bringing our focus from one object to another. ... Pursuits are smooth eye movements that involve following or tracking a moving target. This is especially important for people such as athletes who need to keep their eyes on a moving ball

Canal responses to rotational head movements

Semicircular canals - Rotational acceleration causes fluid movement relative to the canals, as the fluid 'lags behind' (due to inertia) the head/canal - Fluid deflects the cupula, causing responses in hair cells - The three canals are at right-angles to each other, so they can't respond to rotation in any of the three planes

Vestibular Hierarchy

Sensory nerve fibres from the hair cells •project to the vestibular nuclei of the brainstem, then signals go 4 ways -Vestibulo-cerebellar •Some direct projections from vestibular organs to cerebellum •Movement feedback, posture -Vestibulo-spinal •Reflexive balance, including limb movements -Vestibulo-thalamic •Projects to cortex for balance perception -Vestibulo-ocular •Compensatory and stabilising eye movements (vestibulo-ocular reflex - VOR)

Proprioception

The cumulative sensory input to the central nervous system from all mechanoreceptors that sense body position and limb movement.

Recording techniques (live brains)

Single Cell Recording Optical Imaging Non-Invasive (mostly humans) Positron Emission Tomography (PET) and Functional Magnetic Resonance Imaging (fMRI)

Glomeruli

Sites in the brain's olfactory bulb where signals from the smell receptors converge.

glomeruli

Sites in the brain's olfactory bulb where signals from the smell receptors converge.

Snellen acuity

Snellen acuity uses targets to measure visual acuity by means of MINIMUM COGNIZABLE ACUITY.The targets need to follow specific design requirements for the test target. When targets meet the design they are called OPTOTYPES. A typical Snellen optotype subtends 5 minutes of arc with the ability to have five "details" that subtend 1 minute of arc each.

Object-Colour Knowledge

Some objects have typical colour as a central feature that is useful for recognition Colour representations can be accessed both via real colour perception and via implied colour activation • These real and implied colour representations share characteristics but differ in the timing of their neural activation • Object representations are influenced by object-colour knowledge at later, but not at initial stages of visual processing • Single object features are processed before feature-binding occurs which allows for a comparison of visual input with existing knowledge about objects

Outline: Three Stages of Object Perception

Stage 1: Early in visual processing - basic, low level features e.g., orientation Stage 2: Shape representation - Gestalt - Segmentation - Contour integration Stage 3: - View- independent and view-dependent theories - Expertise based effects of visual perception/object detection

Centre-surround antagonism

Stimulation of the inhibitory surround counteracts the centre's excitatory response, causing a decrease in the neurons firing rate.

intersection of constraints

The Intersect constraints determine the closest point and ray intersections with lines, planes, and surfaces. These constraints are different from other constraints in that Modo creates a new constrained item when the constraint is applied, rather than being specified in advance from the selected items.

Multisensory body perception

The Rubber Hand Illusion • Factors influencing the Rubber Hand Illusion

The "Little Person" in your head

The Somatosensory Homunculus - Illustrates somatotopic organisation & cortical magnification - Derived from microstimulation during surgery for epilepsy

Bandwidth

The amount of data that can be transmitted over a network in a given amount of time.

Oculogravic illusion

The apparent backward head tilt and visual elevation experienced during forward body acceleration.

Lemniscal Pathway

The ascending sensory pathway for somatosensory signals from mechanoreceptors.

Barberpole Illusion

The barberpole illusion is a visual illusion that reveals biases in the processing of visual motion in the human brain. This visual illusion occurs when a diagonally striped pole is rotated around its vertical axis (horizontally), it appears as though the stripes are moving in the direction of its vertical axis (downwards in the case of the animation to the right)[1] rather than around it.

Refraction

The bending of a wave as it passes at an angle from one medium to another

Quanta

The bundle of electromagnetic energy that is absorbed or emitted by matter

Fovia

The central spot of the retina, which contains the greatest concentration of cones.

Cornea

The clear tissue that covers the front of the eye

Cone mosaic

The cone photoreceptors represent the initial fundamental sampling step in the acquisition of visual information. While recent advances in adaptive optics have provided increasingly precise estimates of the packing density and spacing of the cone photoreceptors in the living human retina, little is known about the local cone geometric arrangement beyond a tendency towards hexagonal packing. We analyzed the cone mosaic in data from 10 normal subjects. A technique was applied to calculate the local average cone mosaic structure which allowed us to determine the hexagonality, spacing and orientation of local regions. Using cone spacing estimates, we find the expected decrease in cone density with retinal eccentricity and higher densities along the horizontal as opposed to the vertical meridians. Orientation analysis reveals an asymmetry in the local cone spacing of the hexagonal packing, with cones having a larger local spacing along the horizontal direction. This horizontal/vertical asymmetry is altered at eccentricities larger than 2 degrees in the superior meridian and 2.5 degrees in the inferior meridian. Analysis of hexagon orientations in the central 1.4° of the retina shows a tendency for orientation to be locally coherent, with orientation patches consisting of between 35 and 240 cones.

Inferotemporal cortex (IT)

The cortex of the inferior temporal lobe, in which is located an area of secondary visual cortex that is involved in object recognition

Aperture problem

The fact that when a moving object is viewed through an aperture (or a receptive field), the direction of motion of a local feature or part of the object may be ambiguous.

Kinaethesis

The feedback received from muscles and tendon receptors about the body's position in space

Oblique effect

The finding that vertical and horizontal orientations can be perceived more easily than other (slanted) orientations.

Frequency-to-Place Conversion in the Cochlear

The fluid displacement in the cochlear takes the form of a wave travelling along the basilar membrane. ª The wave peaks at a particular location, due to the width & stiffness gradient along the basilar membrane. ª High frequencies show largest vibration near the stapes, at the base of the cochlea ª Low frequencies show the largest vibration near the apex of the cochlea ª This is known as 'frequency-to-place conversion'

Characteristic frequency

The frequency at which a neuron in the auditory system has its lowest threshold.

Ice cube model

The idea that hypercolumns contain a single location column, left & right dominance columns & a complete set of orientation columns.

Specific nerve energy

The idea that neural signals in the senses are differentiated by their pathways in the nervous system, rather than by differences in the nature of the signals themselves.

cross fiber theory

The idea that taste qualities are represented by the pattern of neural activity among an ensemble of neurons; also has application in vision, hearing, and smell.

Representation

The idea that the state of one physical system can correspond to the state of another physical system; each state in one system has a corresponding state in the other

stroboscopic motion

The illusion of movement is produced by showing the rapid progression of images or objects that are not moving at all

Image based segmentation

The image segmentation can be classified into two basic. types: Local segmentation (concerned with specific part or region of image) and Global segmentation (concerned with. segmenting the whole image, consisting of large number of pixels). The image segmentation approaches can be categorized into.

face inversion effect

The inability to detect facial features that are inverted on an inverted face (i.e., the features would be upside down, and very obvious, if the face were turned right-side up), because we are so used to processing faces in the upright orientation.

The Inner Ear

The inner ear contains a small coiled tube (cochlea), filled with fluid. ª The oval window is situated at one end of the cochlea. ª The cochlea is divided in two along its length by the basilar membrane. ª Sound waves impinging on the oval window displace fluid along the cochlea & cause a travelling wave along the basilar membrane.

Cerebral cortex

The intricate fabric of interconnected neural cells covering the cerebral hemispheres; the body's ultimate control and information-processing center.

horopter

The location of objects whose images lie on corresponding points. The surface of zero disparity.

Computation

The manipulation of quantities or symbols according to a set of rules

Inner Hair Cells: Coding Intensity

The range of sound levels over which human hearing can operate (its dynamic range) is >100 dB. ª Individual auditory nerve fibres have a dynamic range of only 20-60 dB. ª Dynamic range = difference between minimum intensity (sound pressure level) to which a fibre responses, and the intensity at the fibre's maximum firing rate ª In order to cover the full dynamic range of human hearing, two groups of auditory fibres have different roles: ª High spontaneous rate fibres respond to lower sound intensities. ª Low spontaneous rate fibres respond to higher intensities.

feedback

The receiver's response to a message

spinothalamic pathway

The route from the spinal cord to the brain that carries most of the information about skin temperature and pain.

cast shadow

The shadow thrown by a form onto an adjacent or nearby surface in a direction away from the light source.

uncrossed disparity

The sign of disparity created by objects behind the plane of the horopter. Images behind the horopter are displaced to the right in the right eye and to the left in the left eye.

Spatial frequency aftereffect

The size, or luminance spatial frequency after-effect (LFAE) is the phenomenon in which adaptation to a luminance grating of given spatial frequency causes a shift in the perceived spatial frequency of a grating away from that of the adapting grating (Blakemore & Sutton, 1969, Science, 166, 245-7).

Middle Ear

The small bones (ossicles) in the middle ear transmit sound energy from the eardrum (tympanic membrane) to the oval window in the inner ear.

monosodium glutamate (MSG)

The sodium salt of glutamic acid (an amino acid).

Contrast

The state of being noticeably different from something else when put or considered together.

Frequency Code

The strength of a stimulus is usually related to the rate at which a neuron sends action potentials

free fusion

The technique of converging (crossing) or diverging the eyes in order to view a stereogram without a stereoscope.

Striate cortex

The visual receiving area of the cortex, located in the occipital lobe.

Neutral point

The wavelength at which a dichromat perceives gray.

Compressive nonlinearity

To accommodate such diverse stimuli, the ear's responsiveness must be nonlinear. The common use of decibels, a logarithmic metric, for the intensity of sound reflects this fact. Nonlinear compression of responsiveness is evident throughout the ear's transduction process. The perceived loudness, the firing rate of auditory-nerve axons, and the basilar-membrane vibration in the cochlea all grow more gradually than the input signal. In the chinchilla's cochlea, for example, sound-pressure levels ranging over 120 dB are represented as basilar-membrane vibrations spanning but 2 orders of magnitude (ref. 2; reviewed in ref. 3). The basilar membrane's responsiveness, defined as the increase in amplitude of vibration evoked by an increment in sound-pressure level, is greatest for threshold stimuli and then declines progressively at moderate to intense levels.

The Somatosensory System

Touch is used to sense physical properties of surfaces such as texture, softness, size and shape Thermoception used to sense temperature Proprioception is used to sense the position of body parts Kinesthesis is used to sense the movement of body parts`

Two-point acuity

Two-point discrimination (2PD) is the ability to discern that two nearby objects touching the skin are truly two distinct points, not one. It is often tested with two sharp points during a neurological examination and is assumed to reflect how finely innervated an area of skin is.

Inflow vs. Outflow Theory

Where does the eye movement signal come from? • •Inflow theory (Sherrington) -Eye muscle proprioceptors sense muscle stretch & send signal to comparator - •Outflow theory (Helmholtz) -Eye movement command from brain goes to eye muscle AND to comparator -"Efference Copy"/ "Corollory Discharge" (they're the same thing)

White matter

Whitish nervous tissue of the CNS consisting of neurons and their myelin sheaths.

Principle of univariance

With regard to cones, the principle that absorption of a photon of light results in the same response regardless of the wavelength of the light

Hyperopia

`A condition in which visual images come to a focus behind the retina of the eye and vision is better for distant than for near objects -- called also farsightedness.

retinal disparity

a binocular cue for perceiving depth by comparing images from the retinas in the two eyes, the brain computes distance—the greater the disparity (difference) between the two images, the closer the object.

Periphery

a boundary line; perimeter; an outside surface

Olfactory bulb

a brain structure located above the nasal cavity beneath the frontal lobes

olfactory bulb

a brain structure located above the nasal cavity beneath the frontal lobes

electromagnetic radiation

a form of energy that exhibits wavelike behavior as it travels through space

Gratings

a framework of parallel or crossed bars, typically preventing access through an opening while permitting communication or ventilation

Spectrogram

a graphic representation of the three major parameters that describe the acoustic characteristic of any sound: time, frequency, and intensity

Our perceptual world is constructed in the brain by...

a huge mass of neurons performing complex, but hidden operations.

Visual cliff

a laboratory device for testing depth perception in infants and young animals

Sound waves

a longitudinal wave consisting of compressions and rarefactions, which travels through a medium

Homunculus

a maplike representation of regions of the body in the brain

Symbolic representation

a mental representation that stands for some content without sharing any characteristics with the thing it represents

Optical imaging

a method for visualizing brain activity in which near-infrared light is passed through the scalp and skull

Positron Emission Tomography (PET)

a method of brain imaging that assesses metabolic activity by using a radioactive substance injected into the bloodstream

Method of Adjustment (MoA)

a method of limits in which the subject controls the change in the stimulus

taste receptor cell

a modified epithelial cell that transduces taste stimuli

efference copy

a motor signal used to predict sensory consequences of an action

Action Potential

a neural impulse; a brief electrical charge that travels down an axon

Rarefaction

a part in a longitudinal wave where the particles are spread apart

lateral geniculate nucleus

a place in the thalamus that receives impulses from the optic nerve

corresponding points

a point on the left retina and a point on the right retina that would coincide if the two retinas were superimposed - for example, the foveas of the two eyes

Steven's Power Law

a principle describing the relationship between stimulus and resulting sensation that says the magnitude of subjective sensation is proportional to the stimulus magnitude raised to an exponent

Selectivity

a process by which some aspects of the world are viewed as important while others are virtually neglected - within each sense, stimuli can vary along various dimensions (e.g. lines vary in location, length, orientation etc. ) - Cells are selective for (i.e. respond most to) stimuli with certain characteristics (e.g. a vertical line) - Response will be smaller the more the stimulus differs from the preferred stilumus - "Tuning" - cell is tuned to 0 degrees (vertical)

Analytical Process

a process in operations management in which raw materials are broken into different component parts

analytical process

a process in operations management in which raw materials are broken into different component parts

Metamer

a psychophysical color match between two patches of light that have different sets of wavelengths

Magnitude Estimation

a psychophysical method in which the participant assigns values according to perceived magnitudes of the stimuli

warmth fibers

a sensory nerve fiber that fires when skin temperature increases

Mechanoreceptor

a sensory receptor that responds to mechanical disturbances such as shape changes, being squashed, bent, pulled; they include touch receptors in the skin, hair cells in the ear, muscle spindles, and others

Harmonic series

a series of frequencies that includes the fundamental frequency and integral multiples of the fundamental frequency

Gratings

a series of light and dark bars; a tool for measuring acuity

Corollary discharge

a signal sent by the brain to the world in advance of or during self-motion to nullify the motion of the scene

Sensory Modality

a system that interacts with the environment through one of the basic senses

Optotype

a target used to measure visual acuity by means of minimum cognizable (identifiable) acuity and that follow a specific design requirement

Single cell recording

a technique by which the firing rate and pattern of a single receptor cell can be measured in response to varying sensory input

Microelectrode recording

a technique used to measure the activity of individual cells

ventriloquist effect

a tendency to mislocalize heard sounds onto a seen source of potential sounds

Olfactory epithelium

a thin layer of tissue, within the nasal cavity, that contains the receptors for smell

olfactory epithelium

a thin layer of tissue, within the nasal cavity, that contains the receptors for smell

Pitch

a tone's experienced highness or lowness; depends on frequency

zero disparity

a type of binocular disparity in which the retinal image of an object falls at corresponding points in the two eyes

crossed disparity

a type of binocular disparity produced by an object that is closer than the horopter - you would have to "cross" your eyes to look at it

foreshortening

a visual effect in which an object is shortened and turned deeper into the picture plane to give the effect of receding in space

Orientation Coding

a)0˚ stimulus Most firing in cells tuned to vertical Firing rate diminishes with preferred orientation of cell b)22˚ stimulus Max. resp. from 22˚ cells c)10˚ stimulus There are no 10˚ neurons ! Firing in 0˚ and 22˚ neurons (and others) can tell us that the orientation was in between Orientation information is not in a single cell, but in the distribution of activity in a population of cells This is population coding d)Prolonged 22˚ stimulus Most firing in cells preferring 22˚ After a while, cells adapt (become less sensitive) e)Now present 0˚ test stimulus Due to adaptation, cells preferring a clockwise tilt fire less than when unadapted Cells preferring anticlockwise tilt are unaffected Distribution of the population activity is shifted anticlockwise Pattern appears tilted anticlockwise f)Adapting to large tilts When adapting & test orientations are very different there will be no effect on perceived orientation

Localization of function

specialization of particular brain areas for particular functions

Blobs

groups of neurons within V1 that are sensitive to color

Lateral Connections

horizontal cells and amacrine cells

Transverse plane

horizontal division of the body into upper and lower portions

interposition

if one object partially blocks our view of another, we perceive it as closer

Missing fundamental

if the fundamental frequency is not equal to the frequency of its lowest component

Presbyopia

impaired vision as a result of aging

Hypercomplex cells

in vision, cells that respond to particular orientations and particular lengths

Composite Effect

in which recognition of one vertical half of a face is difficult when it is combined with the lower half from a different face.

Prosopagnosia

inability to recognize faces

Olfactory cortex

inferior surface of frontal lobe

top-down processing

information processing guided by higher-level mental processes, as when we construct perceptions drawing on our experience and expectations

The McGurk effect - different signals influences identification

integration of mismatching information can change perceptual identification Individual differences • Possibly due to differences in lipreading, detecting audiovisual incongruity or audiovisual integration Effect is stronger when stimuli appear at approx. same time • Some temporal tolerance The effect is stronger when noise is added to uni-sensory component However, effect is not reduced by gender differences face and voice • Overall, findings suggest effect in early stage of phonetic processing

Neural Noise

interference with incoming stimuli

extrinsic

irrelevant; on the outside

Cortical association area

regions of cerebral cortex that receive input from various sensory types, memory stores, and so on, and perform further perceptual processing

Population coding

representation of a particular object by the pattern of firing of a large number of neurons

population coding

representation of a particular object by the pattern of firing of a large number of neurons

High pass filter

resonator that transmits acoustic energy above a specific lower cutoff frequency

Band Pass Filter

resonator that transmits acoustic energy in a range of frequencies between an upper and a lower cutoff frequency

Pacinian Corpuscles

respond to deep pressure and vibration

Free Nerve Endings

respond to pain and temperature

free nerve endings

respond to pain and temperature

autostereograms

result from crossing eyes so patterns are misaligned

Papillae

rough, bumpy elevations on dorsal surface of tongue

papillae

rough, bumpy elevations on dorsal surface of tongue

Olfaction

sense of smell

Gustation

sense of taste

gustation

sense of taste

taste bud

sense receptor in the tongue that responds to sweet, salty, sour, bitter, umami, and perhaps fat

Meissner's corpuscles

sensitive touch receptors in the dermis

olfactory receptor

sensory cell for the olfactory system

Merkel's discs

sensory receptors that convert information about light to moderate pressure on the skin

sensory feedback

sensory signals that are produced by a response and are often used to guide the continuation of the response

Acuity

sharpness of vision

Anisometropia

significant unequal refractive error between two eyes

Otoliths

small crystals in the fluid-filled vestibular sacs of the inner ear that, when shifted by gravity, stimulate nerve cells that inform the brain of the position of the head

Somatotopic

spatially mapped in the somatosensory cortex in correspondence to spatial events on the skin

Reflection

the bouncing back of a ray of light, sound, or heat when the ray hits a surface that it does not go through

Plasticity definition

the brain's ability to change, especially during childhood, by reorganizing after damage or by building new pathways based on experience

Thalamus

the brain's sensory switchboard, located on top of the brainstem; it directs messages to the sensory receiving areas in the cortex and transmits replies to the cerebellum and medulla

Dendrite

the bushy, branching extensions of a neuron that receive messages and conduct impulses toward the cell body

Selectivity definition

the capacity to include some objects but not others

binocular summation

the combination of signals from each eye in ways that make performance on many tasks better with both eyes than with either eye alone

Comparator

the component of the identity control system that compares one's self-concept with one's identity standards

Posterior Vitreous Detachment

the condition where the vitreous separates from the back of the inner wall of the eye

binocular parallax

the degree of disparity between the retinal images of the eyes due to the slight differences in the horizontal position of each eye in the skull

Interaural level difference (ILD)

the difference in level (intensity) between a sound arriving at one ear versus the other

interaural time difference

the difference in time between a sound arriving at one ear versus the other

Azimuth

the direction of a celestial object from the observer, expressed as the angular distance from the north or south point of the horizon to the point at which a vertical circle passing through the object intersects the horizon.

Specific nerve energies

the doctrine that the receptors and neural channels for the different senses are independent and operate in their own special ways and can produce only one particular sensation each

Axon

the extension of a neuron, ending in branching terminal fibers, through which messages pass to other neurons or to muscles or glands

Visually Evoked Potentials

the eyes are stimulated with a bright light or pattern and electrical activity to the visual cortex is recorded through scalp electrodes

Visually evoked potentials

the eyes are stimulated with a bright light or pattern and electrical activity to the visual cortex is recorded through scalp electrodes

Auditory Filter

the filter through which we listen to sounds

gist perception

the finding that we are capable of perceiving the basic properties of a scene in a very brief period of time

Peak contrast sensitivity

the frequency at which the highest contrast sensitivity occurs in a CSF

motion aftereffect (MAE)

the illusion of motion of a stationary object that occurs after prolonged exposure to a moving object

Mitral Cells

the main projective output neurons in the olfactory bulbs

Mitral cells

the main projective output neurons in the olfactory bulbs

amplitude of a wave

the maximum displacement of the medium from its rest position

Channel

the means by which a message is communicated

channel

the medium through which the message is sent

Just Noticeable Difference (JND)

the minimal change in a stimulus that can just barely be detected

Emmetropia

the normal relationship between the refractive power of the eye and the shape of the eye that enables light rays to focus correctly on the retina

Frequency

the number of complete wavelengths that pass a point in a given time

Brainstem

the oldest part and central core of the brain, beginning where the spinal cord swells as it enters the skull; the brainstem is responsible for automatic survival functions

brainstem

the oldest part and central core of the brain, beginning where the spinal cord swells as it enters the skull; the brainstem is responsible for automatic survival functions

Apparent motion

the perception of movement as a result of alternating signals appearing in rapid succession in different locations

diplopia (double vision)

the perception of two images of a single object

tilt aftereffect

the perceptual illusion of tilt, produced by adaptation to a pattern of a given orientation

Colour Misconceptions #2

•"White and black aren't colours: they're shades" - -Colour is an experience of a combination/pattern of ls of light - -Therefore white & black qualify

Place code

the process by which different frequencies stimulate neural signals at specific places along the basilar membrane, from which the brain determines pitch

absorption of light

the process by which matter absorbs radiative energy

Accomodation

the process by which the eye's lens changes shape to focus near or far objects on the retina

Stereopsis

the process by which the visual cortex combines the differing neural signals caused by binocular disparity, resulting in the perception of depth

Dynamic range

the range of exposures that may be captured by a detector

Critical Bandwidth

the range of frequencies conveyed within a channel in the auditory system

Extrastriate Cortex

the region of cortex bordering the primary visual cortex and containing multiple areas involved in visual processing

panum's fusional area

the region of space, in front of and behind the horopter, within which binocular single vision is possible

Receptive field

the region of the sensory surface that, when stimulated, causes a change in the firing rate of that neuron

Odorant receptor

the region on the cilia of olfactory sensory neurons where odorant molecules bind

Factors influencing multisensory processing

• Factors first studied in superior colliculus responses Inverse effectiveness: As stimulus effectiveness increases, the benefit from spatiotemporal synchronous visual and auditory stimuli decreases Effectiveness of unisensory stimuli (Inverse Effectiveness): Multisensory interactions are more likely or stronger when the constituent unisensory stimuli evoke relatively weak responses when presented in isolation • Behavioural Evidence: McGurk effect increases when adding noise to unisensory signals Other factors are relevant to decide what signals belong together ('binding') • These are: temporal synchrony, spatial correspondence, synasthetic congruency • These factors are typically studied by introducing conflicts and testing how such conflicts affect multisensory perception Temporal synchrony • Multisensory interactions are more likely or stronger when the constituent stimuli arise at approximately the same time • Degree of temporal tolerance: differences in propagation and processing time for different senses (example: McGurk effect) Spatial correspondence Multisensory interactions are more likely or stronger when the constituent unisensory stimuli arise from approximately the same location. An auditory signal presented in the same location as the subsequent visual target leads to faster RTs and less errors for visual target detection. Compared to an auditory signals presented in a different location (ca. 100 cm apart, in the opposite visual field). Synesthetic congruency • We all have a tendency to 'map' certain stimulus features across the senses systematically • For example: we match a high-pitched sounds with a small bright object that is located high up in space

Anatomical tracing studies

• Feedforward connections from unimodal & multisensory cortex (accounted for by standard view) • Also direct connections between unimodal cortices • Primary visual cortex receives projections from auditory cortex Auditory association cortex receives projections from both primary auditory & somatosensory cortices • Feedback connections from multisensory to unimodal cortex • Conclusion: Highly interactive network that integrates information from the senses for conscious perception

The Cone of Confusion

• How do we resolve the cone of confusion? • Head movements for pure tones • Frequency filtering at the pinna also helps resolve complex tones

The Cone of Confusion

• ITD & ILD can be ambiguous • Each ITD & ILD corresponds to two possible azimuths (i.e. can't tell front from behind) • Also, binaural cues give no information on elevation • As a result, a sound producing a particular ILD & ITD could originate from anywhere on the surface of a cone

Models of Loudness

• Individual Auditory Nerve Fibres - Auditory nerve fibres are tuned to a characteristic freq (CF), but respond a little to neighbouring freqs - For a given auditory nerve fibre, you need more intensity at freqs other than the CF to get the same amount of firing as you would to a CF sound • Neighbouring neurons - At detection threshold for a particular freq, only the fibres with the appropriate CF will fire above their spontaneous rate - As intensity increases, neurons with CFs just lower and just higher than the stimulus freq will become excited - The higher the intensity, the louder the sound because more neurons are firing

Standard view of multisensory processing:

• Initial processing in unimodal sensory cortex • Subsequent processing in multisensory convergence zones • > Feedforward connection/processes • BUT • Recent evidence for multimodal responses in primary sensory areas • > Feedback and lateral connections

Evidence for multisensory processing

• McGurk effect (stimulus identification) • Cross-modal cuing (stimulus detection) • Ventriloquism (stimulus localisation)

Mechanisms of multisensory processing

• Multisensory convergence zones (feedforward processes) • Multisensory responses in 'unisensory' areas (feedback & lateral connections) • Factors influencing multisensory processing (inverse effectiveness, temporal synchrony, spatial correspondence, synesthetic congruency)

Summary Object perception

• Object perception is effortless but the process is complex • Features must be detected, integrated, and interpreted • Inbuilt grouping biases and experience can play important roles in the visual processing of objects

Monaural Sound Localisation

• Pinnae filter incoming sound waves • Important for sound source localisation on the vertical plane

Summary 2

• Pitch of a sine wave is coded by frequency-to-place conversion (place theory) and rhythmic firing pattern of cochlear cells (timing theory) • Pitch of complex tones can be somewhat explained by temporal and pattern recognition theories • Loudness is proportional to the total neural activity evoked by a sound in the auditory nerve • Duplex theory of sound source localisation: - ITDs good for low frequencies; ILDs good for high frequencies • Pinnae important for vertical sound source localisation

Preferential Looking

•"Acuity Card" -central peep-hole -a grating on one side -Either a blank patch, or a different grating on the other side - •Experimenter looks through the peephole to see which stimulus the baby looks at • •Then checks which side the stimulus was on

Colour Misconceptions #4

•"Colour blind people see only black and white" • •Depends what you mean by "colour blind" -The majority of colour deficient people (dichromats and anomalous trichromats) can discriminate many colours -Monochromats (only one cone, or only rods) and those with complete Cerebral Achromatopsia can only discriminate light from dark (truly "colour blind")

Colour Misconceptions #3

•"Red, Yellow and Blue are the primary colours" •"Red, Green and Blue are the primary colours" •It depends what you mean by "primary" -For mixing colours, any set of 3 reasonably different single wavelengths can be mixed to match any single l of light, so any of these combinations could be considered "primary" -If we're talking about the 3 different photoreceptor types, we should really refer to Short (~420nm), Medium (~530nm) & Long (~560nm) l -tuned photoreceptor types. These ls don't necessarily look like typical blue/green/red

Colour Misconceptions #1

•"There are 7 colours: Red, Orange, Yellow, Green, Blue, Indigo & Violet" - -Newton did divide the spectrum into 7 different named categories, but in reality the spectrum is a continuum -Any division into categories is to some extent arbitrary -Besides, what about brown? •(It's actually just dark yellow-orange - i.e. lower intensity at approx. 600nm)

Motion Detectors further info

•Correctly timed/spaced "flashes" set off a directional Reichardt detector, and look like real motion in that direction •What happens if there are 2 "double-flashes" (simultaneous flashes, one over each of the receptors, repeated)? •Motion is signalled in BOTH directions -t1 flash at A combines with t2 flash at B to signal rightward motion -t1 flash at B combines with t2 flash at A to signal leftward motion •Do we see motion? Not really (demo) •This is a bit of a problem for the Reichardt detector model •Can we improve our Reichardt detector to account for human performance? •Reichardt detector should have no response if there are 2 "double flashes" (see previous slide) •Do this by use of a "comparator" unit comparing responses from each direction-selective motion detecting unit (AND cell) -The larger directional signal wins -If activity is equal in each directional motion detector (AND unit), the comparator signals no motion -This new model accounts for our observations so far •So far, our hypothetical "Reichardt detector" model accounts well for human performance •There are other popular models that can also account for these phenomena -e.g. gradient models, motion energy models, etc. -They're too complicated for this course •For the following phenomena, it doesn't matter which of these we use for the early stages of motion detection (same predictions) •If opposite direction signals are compared, then this can be referred to as a "ratio model" (regardless of what kind of detectors give the input)

Causes of Prosopagnosia

•Damage to IT can cause "prosopagnosia", or "face blindness" •A selective impairment of visual face processing abilities -No generalised memory deficit •People can be recognised from voice, or semantic information •No problems recognising objects •Some prosopagnosics seem to have a perceptual deficit -Can't match, copy or recognise faces -They report faces looking flat, featureless, expressionless... •Many seem to have a memory problem -Can copy or match faces (perception is OK), but cannot recognise them

Young-Helmholtz Trichromatic Theory of Colour Vision

•Developed many decades before neurophysiologists discovered & measured the 3 separate cone types -There are only 3 receptors, each broadly tuned to l -Perceived colour depends on the relative strength of their activation

Colour Deficiency(not really Colour Blindness)

•Different types associated with different cone types •Anomalous Trichromats -Have 3 types of cone, but responses are different from most (normal) people, due to deficiency in one cone type •Protanomaly (red/long cone), Deuteranomaly (green/medium cone), Tritanomaly (blue/short cone) •Dichromats -Lack one cone type entirely •Protanopia/Protanopes (red/long cone), Deuteranopia/Deuteranopes (green/medium cone), Tritanopia/Tritanopes (blue/short cone)

Explaining the MAEusing the ratio model

•Direction-selective units tuned to opposite directions are connected to a 'comparator' (It could be something like the Reichardt detector described earlier) • •Direction firing most is the perceived direction ● a)Stationary stimulus Both "Up" and "Down" units respond at baseline Comparator registers no difference between the two Þ we see no motion b)Downward motion stimulus •"Up" detector fires at baseline. "Down" motion unit fires rigorously. •Comparator registers more activity in "Down" than in "Up" detectors. Þ We see downward motion. •ADAPTATION: As motion continues, activity drops for "Down" detector. • c)Stationary stimulus •"Up" detector continues at baseline. Adapted "Down" detector activity now lower than baseline. •Comparator registers more activity in "Up" than "Down" detectors. Þ We see upward motion

Is Motion Sensed Directly?

•Do we just judge position and judge time separately, and divide one by the other? -No - precision for position & time perception is not good enough to account for precision in speed discrimination •Instead motion is sensed directly, by specialised mechanisms (as shown by adaptation experiments) -E.g. the Motion Aftereffect (MAE) (More on that later)

An Adaptation Model of Body Image Disturbance?

•Does visual adaptation apply to "real-world" body size/shape misperception? ⎼Exposure to "thin ideal" images in the media causes aftereffect of OVERESTIMATION (mainly of fat mass) ⎼Exposure to idealised muscly bodies causes aftereffect of UNDERESTIMATION (mainly of muscle mass) ⎼Studies ongoing in our lab and others

Mirror Stereoscopes

•E.g. Wheatstone Stereoscope (1838) •Mirrors angled at 45º in front of observer •Half-images (E, E') and mirrors (A, A') should be arranged to simulate the appropriate vergence angle •Images are reversed •One observer only

Multiple Spatial Scales

•Each image contains information at multiple spatial scales •Low SFs carry course scale info •High SFs carry fine scale info

Perceived Depth & Perceived Size Constructs

•Emmert's Law -For a given retinal image size, perceived size of object is proportional to perceived distance •Could this explain some visual illusions (e.g. Ponzo Illusion)? •Misapplied Constancy Scaling -Visual system assigns a depth to the object -Perceived size is calculated with respect to this depth percept -If the depth percept is inaccurate, an error in perceived size will be predicted •Ames room •Julian Beever's Pavement Art -Figures on the left look small because depth is underestimated

Face adaptation examples

•Example #1 Viewpoint -Get photos of subjects from different viewpoints -Adapt to a face oriented slightly to the left -Observe a face in frontal view -Aftereffect: face appears to be facing slightly to the right - •Example #2 Sex -Create an average face by "morphing" together the face of a man and a woman (50%:50%) -Adapt to the face of a male -Observe the average (50%:50% morph) face -Aftereffect: face appears distinctly more female

Gustation Adaptation

•Exposure to a taste can affect the perception of a later taste •Adaptation to one sour taste reduces the apparent intensity of other sour tastes •Cross Adaptation -Adaptation to... •a sweet taste causes water to taste sour •a sour taste causes water to taste sweet & reduces the intensity of some bitter tastes

Internal and External Features

•External Features (hair/hairline, chin, ears, beard, etc.) -Change over time •Intentional (fashion/disguise) •Unintentional (old age!) -Unreliable at signalling identity - •Internal Features (eyes, nose, mouth) -Relatively stable over time -More reliable at signalling identity

Dual Process Theory

•Hurvich & Jameson (1957): dual process theory wherein trichromatic receptors (cones) feed an opponent process -Luminance (B&W) = Long + Mid or Red + Green -Red&Green = Long ÷ Mid or Red ÷ Green -Yellow&Blue = (Long + Mid) ÷ Short or (Red + Green) ÷ Blue

Fixation, Fusion & Focus

•Fixation: -the act of directing your gaze towards something so that its image falls in the middle of your fovea. -If you fixate an object with both eyes, you "verge" (or "converge") on it - see vergence cue to depth. - •Fusion: -the phenomenon that some objects with small disparities are not seen as "double" (diplopic) - instead their images are "fused" into one - •Focus: -if the current state of the lens causes light rays spreading from a point at a given distance to meet at a single point on the retina, objects at this depth will be "in focus", i.e. will appear "sharp" (see "Focussing", in LE&B lecture, and "Accommodation" and "Blur", later in this lecture)

Flavour

•Flavour is not the same as taste •Flavour incorporates many different senses: -Gustatory -Olfactory -Also Visual, Somatosensory, etc. •Food in the mouth stimulates the olfactory epithelium via the retronasal route (air passage behind the palate) -Try eating/drinking while holding your nose (stops air flow to the olfactory epithelium, even via the retronasal route) •Processed in the Orbitofrontal Cortex (OFC) ??? -A multimodal brain area: first site for taste-smell signal combination -Bimodal neurons respond to both the taste & smell (or taste/sight, etc.) of certain fruits

Wagon Wheel Effect example

•For TV/Cinema, there is no motion: only separate frames featuring image displacements • •Imagine a wheel with 4 spokes (see right), which is shown in 2 film 'frames' (T1 and T2) -Slow motion means small displacements per frame (e.g. an angular displacement of 10deg per frame) -Faster motion means larger displacements (e.g. 35 deg per frame) -Clockwise motion involves clockwise displacements; anticlockwise involves.... GUESS?! -So far, we see exactly what's there... •For wheels, each spoke looks the same -Q1: What if the speed involved exactly a 90deg displacement? -A1: Wheel would look identical in frame 1 & 2 - no motion perceived at all. -Q2: What if the displacement between frames is 45deg? -A2: There would be no way of telling whether it moved clockwise or anti-clockwise. •A 70deg clockwise displacement looks the same as a 20deg anticlockwise turn •We tend to perceive the motion corresponding to the shorter displacement, hence fast motion can appear "backwards"

Perception: Taste Dimensions

•Four basic taste dimensions identified in the early 1900s, based on perceptual classification -Henning's taste tetrahedron places them on a geometrical shape to indicate combinations •The classification is consistent with modern physiological data on neural responses •Except... -A fifth taste — umami — has recently been proposed -Described as "yummy", "savoury", "meaty" -Associated with monosodium glutamate (MSG) -Receptor identified in 2000 (Chaudhuri et al. 2000) -Role in perceived taste is unclear

Gustation Selectivity

•Four categories of taste neuron have been found, maximally responsive to -Sugars (sweet) -Salts -Acids (citrus fruits - sour) -Plant alkaloids, e.g. quinine (bitter) •Infer that each taste cell mainly houses receptors of one type •Some responses to other chemicals Nowlis and Frank (1977) •Encoding of taste -Taste primaries? •Each "channel" signals its own property alone -Cross-fibre theory (population coding)? •Taste signalled by the overall pattern of firing over all 4 channels

The Retina

•Fovea (Macula) -The thing you're looking at is imaged here -Many receptors, no blood vessels - •Optic Disc -Ganglion cells axons leaving the eye through the optic nerve -No receptors here (blind spot)

Vergence

•Generally, fixated objects fall on our fovea in each eye •Each eye has to be pointing in the correct direction •The angular position of each eye could be used to calculate the depth of the fixated object - vergence -For long distances, vergence angle will be small (top image); For short distances, it will be large (bottom) -This can give weak depth information (Backus & Matza-Brown, 2003) •Binocular, Non-pictorial, Oculomotor, Metric

Gratings/Optotypes

•Gratings lose their appeal for children at about 12months of age •Introduce more interesting stimuli •Optotypes are pictures drawn with balanced black-white-black lines of a particular spatial frequency •When SF is high enough, the black & white portions "cancel" each other out, and fade into grey background

Hierarchies: Cortical Physiology

•Gustatory nerve axons terminate in the brainstem -Coding of the 4 taste channels is thought to be preserved at least up until the brainstem (Delcomyn, 1998) •Projections from the brainstem travel to the cortex via the thalamus, & to the amygdala •Coding in primary gustatory cortex (aka Insula cortex) is largely a MYSTERY! •Insula cortex projects to the multimodal Orbitofrontal Cortex (OFC)

The Wagon Wheel Effect

•Have you ever noticed how car wheels sometimes appear to spin backwards in movies? •This is the wagon wheel effect - originally seen on stage coaches in Westerns •Wheels can also appear stationary, or to have the wrong speed •Similar effect can be seen for many periodic motion stimuli

Fourier Analysis

•How to make a square wave (sharp edges) using sine waves (blurry stripes) •Start with one sine wave •Add a sine wave with 3x the spatial frequency, but 1/3 the contrast •Add another with 5x the SF, but 1/5 the contrast •Next, 7x SF, 1/7 contrast... •...and so on •Series is infinite (but our visual acuity isn't)

Synthetic Nature of Olfaction

•Humans are unable to identify newly learnt components in odour mixtures with >3 parts (Laing & Francis, 1989) -As in this picture, it's just a mess! •But training & experience can allow some ability to recognise odours, by allowing receptor outputs to be grouped (Wilson & Stevenson, 2003) -Like this...! •Unlike in vision, information from individual receptor outputs (i.e. the dots) are still not accessible

Population Coding

•Humans can recognise ~10,000 odours •How is this possible with only 500-1000 different receptor types? •Answer: Population coding (Malnic et al. 1999) -Stimulus information is encoded not simply by which cell is firing most, but by the pattern of firing throughout the entire neural array -Each olfactory mixture is represented by a different pattern of activity across receptors/mitral cells (Sicard & Holley, 1984)

Composite Face Effect

•Humans can't avoid processing faces as "wholes" (Holistic processing) Composite Face Effect (Chimaeric Faces) -In the first slide, the top & bottom halves of two different faces had been aligned -The image makes a new "whole face" and humans are less able to process it as 2 halves •e.g. ask participant to match top half with an appropriate other image (perception), or to identify it (memory) -If you misalign the faces, they no longer form a new "whole", and you can then process them separately •Matching performance is much better for misaligned than aligned halves

Terminators are not all equal!

•Terminators signal either... -Edge of an object (INTRINSIC TERMINATORS) -The occlusion of the object by another, closer object - i.e. the object doesn't end here - it continues behind the occluder (EXTRINSIC TERMINATORS) - •Intrinsic terminators are the real edges of object -Motion signals give true object direction - •Extrinsic terminators are caused by occlusion & are not the real edges of the object -Motion signals are misleading & should be ignored •Heed Intrinsic terminators •Ignore Extrinsic terminators •Depth cues can tell us which terminators are Extrinsic, and which are Intrinsic: -Occlusion -Disparity -Shadows •Aperture problem solved with surface segmentation in mind

Illusions Explained Herman Grid

•The Herman Grid •Illusory dark patches at the intersections • •Less noticeable closer to the fovea

The Horopter

•The Horopter -A line of all possible locations where an object's half-images fall on corresponding points -Defines locations at which objects have zero disparity •Objects nearer than the horopter are said to have a crossed disparity (think of going cross-eyed) •Objects further than the horopter have an uncrossed disparity

Blur

•The object being viewed foveally is usually in focus •Blur varies with depth compared to viewed object (depth of field) •BUT both near & far objects are blurred •Look at the edge between regions -Occlusion means that the edge takes on the blur property of the near object -Blurred edge => blurred object is near -Sharp edge => sharp object is near •Monocular, Pictorial, Visual, Metric

Vestibular Perception

•The oculogyral illusion -Spin round repeatedly, then stop -Illusory movement of the body and of stationary objects occurs -Due to inertia, fluid in the semicircular canals decelerates more slowly than the canals when spin stops -The resulting shear is in the opposite direction to that produced by the original rotation - •The oculogravic illusion (right) -When the body undergoes linear acceleration, an illusory impression of body tilt occurs -Linear acceleration and static head tilt both trigger responses in the otoliths -Responsible for plane crashes during take-off from aircraft carriers

The Electromagnetic Spectrum

•The spectrum Newton observed is only a small part of the broader electromagnetic spectrum •Wavelengths (ls) appear different in colour •Visible ls range from 400-700nm (nanometres) •1nm = 1m x 10-9, i.e. a millionth of a mm •Many ls are not visible to humans

Adaptation & Face Representations

•These adaptation effects are what you'd expect if the brain represented faces in populations of neurons tuned to different levels of a face property •Remember tilt (orientation), or spatial frequency adaptation? •This does seem to be the case to some extent (e.g. monkey IT cells tuned for viewpoint), but studies are ongoing

Colour Constancy & The Dress

•To show colour constancy, our visual systems must be able to estimate the spectral content of the light source so that it can "subtract" it •Problems arise when the light source is unclear •If you assume a light source that is "warm" (i.e. yellow-biased, such as artificial indoor lights), the dress looks black/blue •If you assume a light source that is "cold" (i.e. blue-biased, such as indirect daytime illumination), the dress looks white/yellow.

Age Related Macular Degeneration (AMD)

•UV light absorbed by macula which can damage retina •Yellow deposits ("drusen") in macula •Loss of central vision •Major cause of blindness in over 50s •Dry AMD and Wet AMD •No treatment or cure •Prevention only -Wear sunglasses with UV filters -stop smoking -eat brightly coloured vegetables, rich in antioxidants (???)

•Do we just see the colour corresponding to the l that's there?

•Unfortunately, it's not that simple -Rarely in nature is there one single pure l •As in hearing & spatial vision, there's a spectrum of waves with different intensities at different ls -The link between colour experience and a single l doesn't tell us how we perceive colour

Face Perception

•Unlike adults, babies can discriminate monkey faces as easily as human faces •This ability is lost by 10 months •Similar effects for discriminating human faces from different racial groups •i.e. Unlike adults, babies don't suffer from the "other race effect" •"Perceptual Narrowing" •Similar in other modalities, e.g. audition •Babies can discriminate many speech sounds, whereas adults can only discriminate those used in their language •"Use it or lose it"

Motion Perception

•Use "odd one out" paradigm -Similar to preferential looking, but withmore options •Develops over a long time beginning at 10-12 weeks •Medium speeds detected earliest •The special case of looming - detected as young as 2 weeks!

Visual Change

•Use distorting goggles (e.g. Stratton, 1897) -Turn world upside down -Disconnect of vision & proprioception -Eventual adaptation •Compensation or recalibration? -Readjustment required after removing the goggles •What if observer is passive while wearing goggles? -Distorting prisms and wheelchair pusher (active) / pushee (passive) experiment -Active observer adjusts more quickly •=> As in kitten carousel, interaction with environment is important

Perspective

•Uses essentially the same information as familiar size cue •Don't have to recognise the object, but assumptions are still made •Linear Perspective (convergence) -Assume lines are parallel -NB: Mather distinguishes perspective from compression/foreshortening - most other authors say they're the same •Detail Perspective (texture gradient) -Assume texture elements are of similar size •Monocular, Pictorial, Visual, Metric •Perspective can be "forced" to make you misperceive depth •Sports field advertising •Anamorphic art •Etc.

V1 Organisation

•V1 is organised into orientation columns -In a column, cells have same preferred orientation •Also columns of ocular dominance -In a column, cells take inputs from the same eye •Both eyes & 180˚ of orientation makes a hypercolumn -(Almost) everything you might want to know about a small area of visual space This is known as the "Ice Cube" Model

Extrastriate Cortical Visual Areas

•V1 projects to other important extra-striate brain areas •V2 •V3 •V4 (colour?) •V5/MT (simple motion?) •MST (complex motion?) •Each is retinotopic (except MST) Cells next to each other have retinal receptive fields next to each other