Perception

three main factors that affect CSF

1. light level (shifting from photopic to scotopic causes a systematic decline in CSF) 2. Age CSF gets less sensitive with aage also 3. disease, things with catacts and myopia

two essential functions of optics

1.) form an image on the retina 2.) transduce signal into neural activity

polarization- how obtained?

1.) scattering - polarization along a single plane, the sky 2.) transmission through crystals, polaroid film. absorbs more light in one plane than in another. 3.) reflection, unpolarized light can be reflected back and then become polarized.

speed of light in a vacuum

299,792 hm/hour, one of nature's fundamental constants

critical flicker function

CFF, frequency at which temporal changes are undetectable, capable of detecting changes up to 60 Hz per second, after this events are uniform

structuralism

William Wundt introduced this theory in order to explain consciousness, mental experiences result from a set of elementry building blocks assembeld in the mind and visual perception arises from definable components (problem: too subjective)

reichardt detector

a simple neuronal circuit that creates the property of directional selectivity because two neurons detect stimuli through adjacent higher level neurons.

wavelength

a single cycle represents the segment of the wave before it repeats itself.

foveal pit

a small depression in the fovea that makes the thickness in the center of the retina relatively less. all neurons are shifted to one side to allow incoming light rays access to photoreceptors, makes the image quality better at the fovea because there is less change for distortion and scattering

recognition by components

a solution to the binding problem that says that visual objects are parsed into simple 3d volumes that are assembled to create mental representations. Advantage is that basic structural elements display view invariance

Retina (details)

a thin film of cells that lines the inside back wall of the eyeball, thought of as in 3d.

color opponent neurons

There are four types in the LGN, have the exact same center surround profile as On/Off type neurons but with opposing chromatic profiles instead

ocular dominance scale

Type 1 neurons are driven by contralateral eye primarily and type 7 neurons are primarily driven by the ipsilateral eye.

L cone

absorbs peak around 560 nm, long wavelength cones

principle of univariance

absorption of each photon in a cone produces excatly the same response regardless of wavelength, L cones cannot absorb short wavelengths

visible light

accounts for a small portion of the spectrum, sensory function is limited to between ultraviolet and infrared rays. different wavelengths produce different colors of visible light

NEW THOUGHT ON DORSAL AND VENTRAL

actually the action and perception streams

motion adaptation

adapt to a stimulus and neurons firing enter a state of reduced responsiveness and become slightly sluggish, a motion impression in opposite direction happens as a result of spontaneous firing.

rhodopsin bleaching (rods)

after rhodopsin absorbs light it is rendered temporarily unable to absorb anymore light, this is "bleached" and eventually rod receptors become blidn

Snellen chart

alphabetic characters need to be sufficiently large in order for their identity to be resolved

color signal

amount of energy contained in the light is multiplied by the amount reflected by the object, produces a new plot (perceived color)

photoreceptor array

an array of photoreceptors are embedded in the fibrous matrix that holds the eyeball together (sclera) this is the photoreceptor array

minute arc

angular measure, people with perfect vision can resolve a minimum angle of resolution with one minute arc

amacrine cells

another group of neurons that participate in generating the surround response, large number of amacrine cell types, most functions are very poorly understood.

saturation

any hue can vary in terms of it's saturation or purity, full saturation is the most intense and bright, unsaturated is grey

complementary

any pair of colors that produces white when mixed, all spectral colors on the color circle have complements

accretion and deletion

appearance or disappearance of objects behind an edge, like a curtain, that has an occluded object showing more or less of itself

disparity selectivity

area V1 has three classes of neurons dedicated to classifying information from each depth percept, including zero disparity, crossed and uncrossed.

double opponent neurons

area V1 primary visual cortex, display both spatial and chromatic opponency, provide a strong response to isoluminance conditions

feed forward projections

area V1, directionally selective neurons go to higher cortical areas, not always direct and sequential connections

cytochrome oxidase blobs

areas rich in cytochrome oxidase are arranged at the top of ocular dominance columns and thus are correllated with high neuronal activity

Ricco's law

as a spot size becomes larger a greater number of photoreceptors are stimulated and more signals converge upon a ganglion cell, overall inetnsity needed to generate the same output gets smaller (Ricco's law, light intensity * stimulation area = critical level)

ciliary muscles

associated with the lens, cause blur spots on the retina.

pictorial cues

based on stationary optical information contained in the two dimensional scenes or pictures, based on physical unchanging factors

newton's prism breakthrough

beam of light passes through a prism, shows that it is actually made up of a rainbow of colors.

white light is neutral?

because of the additive properties of sunlight at different wavelengths

optical image at the fovea

because of the foveal pit, quality is greatly enhanced since it is not subject to scatter or light distortion

extromission theory

belief that the eye was the device that transmitted light to the outside world

two features of mamammlian eye movement

binocular in nature and extremely precise

corpus callosum in cyclopean perception

binocular neurons are activated under conditions where images project separately to the two hemispheres, they integrate visual information between opposite hemispheres through the corpus callosum and also integrate sensory information across midline

properties that arise in V1

binocularity, orientation selectivity, directional motion selectivity, color contrast detection.

dual process theory

both trichromatic receptors and color opponency are right, but they occur at different stages in color processing

size constancy

brain perceives objects in terms of physical reality and not on the basis of retinal image size

comparator

brain structures that receive the motor copy, correlates sensory and motor signals to create position constancy

horizontal cells

branch out laterally and make contact with adjacent photoreceptors. Intermediate neurons that are situated between the photoreceptors and ganglion cells, generate the center surround response

microspectrophotometry

breaks down spectrophotometry into individual isolated cone photoreceptors, confirms the existence of three different types of cone photoreceptors that have their own absorption spectrums

view invariance

can tell what an object is no matter what view we are looking at it from.

optic nerve

carries information from one eye, the fiber bundle emerging after the optic chasm has information from both eyes. the right side of the brain processes the left side of the visual field and vice versa

spatial sampling

cells above the photoreceptor are layered in exclusivity so tht one photoreceptor feeds into One bipolar cell and then one ganglion cell. THis is ideal for spatial sampling since one light detector is connected to one output.

spontaneous activity

cells often fire in the absence of any photons because htey are optimized to signal overall light levels and differences in light stimultion across the retina.

pigment epithelium

cells that contain pigmented material that absorbs stray light that did not get captured by the photoreceptors. albinos lack these which causes them to not absorb stray light

lightness

center surround antagonism is responsible for the visual system's preference for analyzing in terms of light contrast

orientation selectivity

center surround profiles are rectangular instead of circular so that you can sense orientation of a stimulus as well as contrast

lightness contrast

central disks in both stimuli reflect the same amount of light and have the same lightness intensity, but one may appear more intense if surrounded by a less contrasting color.

accommodation

change in the curvature of optical surfaces in the lens that account for changing distances

phototransduction

changing light energy produces an unconventional outcome in electrical activation, doesn't follow necessarily the same pattern as other action potentials

binocularity

characteristic of v1 neurons to receive input from both eyes, light stimulation from one or both eyes, increased firing rate when both are stimulated. (lgn driven by monocularity)

midget ganglion cells

characterized by small size and compact dendritic fields, found in and around the fovea

Reichardt detector advantage

circuit relies only on temporal summation of signals from two detectors to produce directional selectivity, preference for another direction of movement can be easily created by placing interneurons

waterfall illusion

cliff behind a waterfall appears to move up really quickly after viewing falling water for a certain amount of time

accommodation of closer objects

closer objects need more accommodative power (until they reaach a near point)

monochromacy

color blindness, the only true form

dichromacy

color deficiency, occurs in small percentages of the population

chromatic nature of light

color perception is generated by light itself and sunglight is made up of component colors

ocular dominance colums

columns with eye preference, the LGN projections to layer 4c are separated in terms of eye representation with left and right eye projections arriving in alternating sectors of 4c, these columns have neurons with every possible orientation preference and they span the thickness of the cortex

binocular fusion

combines two retinal images to produce a unified picture of the visual scene, we don't perceive two different world views but a single mental image that is referred to as cyclopean perception

lateral inhibition

commonly observed property of the nervous system, mechanism allows ganglion cells to inherit the property of center surround antagonism and become endowed with a receptive field that is optimized for light contrast

parallel visual pathways

compartmentalization allows the brain to perform it's operations more smoothly, different parts of the stimulus are encoded by different networks of neurons

dorsal visual stream

computes the dynamic aspects of vision and the spatial relationships of objects to guide motor function, visual aspects of the parietal lobe that form the stream (in addition to motion areas)

optimal dispaity

condition where binocular neurons in V1 are tuned to a particular disparity value and they are most optimally going to fire when that is the dispartity value being observed

distribution of cones

cones are everywhere since they contribute to day vision,

compare sensitivity curves of rods and cones

cones have a higher activation threshold than rods, there should be an increase in light detection threshold at the fovea.

emission spectrum (color)

continuous profile of energy across the full spectrum of visible wavelengths from sunglight, breaks down a white light into it's components

saccades

controlled by the superior colliculus, rapid orienting movements of the eyeballs from one object to another (reading)

convex lens

convergent properties, lens bends outwards, causes the normal to be oriented so that light rays are refracted in

presyopia needs what lens?

convex lens for additional refractive power, reading glasses are a common fix for this problem

visual cortex

cortical areas developed to the neural processes that accompany visual analysis, occipital lobe at the back of the brain, but visual information travels through all parts of it

free fusion

crossing the eyes to produce a fused and overlapped imge

presyopia

crystalline lens loses it's elasticity and begins to harden due to the protein fibers inside, afflicts everyone beginning in their 40's, gradual loss in lens elasticity causes a loss in accommodative value, near objects appear blurred

agnosia

damage to ventral pathways results in a loss of function in identifying objects but no issues with signt, proves that the ventral stream has a significant perceptual function

Area MT

dedicated to motion processing, vast majority of neurons that are directionally selective.

McCullough Aftereffect

demonstrated by viewing each grating then shifting to the other

contingent aftereffects

dependent on TWO aspects of a stimulus, such as orientation and color.

blindsight

despite losing ability to see, people can still detect light and where it comes from. believed to be controlled primarily by the SC and pulvinar

position constancy

despite moving our eyes, visual world is stable and does not appear to move despite self-generated eye movements

point spread functions

detection abilities to resolve two individual points of light limited by the extent of the blur spots they produce, the two PSF's must be sufficiently spaced apart before they can be physically distinguished

dark adaptation

detection threshold for a small light spot is measured at various times after bleaching, cones follow a quicker pattern for adaptation than cones. they take much longer to be unbleacher, which is why we take longer to adjust to a dark environment than a light one!

spatial frequency

determined by the cycles per span, one with three full cycles of a sine wave is said to have 3 cycles/degree. The greater the spatial frequency the more spatial detail an object has.

aperture

diameter of the pupil. iris is fully open, the retinal image is defined by a large cone of rays so there are more blur spots.

perfectly stable images in the retina

disappear because visual system adapts

layer 4c

distinctive because it is where the LGN fibers terminate and synapse onto v1 neurons, thus visual processing in the primary visual cortex begins in 4c.

concave lens

divergent properties, two surfaces that are bowed inwards, light bends at the first surface and then again at the second surface, things diverted away

SC functional division

divided into superficial and deep layers, where retinal fibers project to form a retinotopic layout of the contralateral visual field in superficial layers.

median plane

divides left and right sides of the body, movement around known as Yaw, Z axis

superior temporal sulcus (STS)

divides temporal lobe into superior temporal cortex and inferior temporal cortex, area IT

Off activation and bipolar cells

do not show this effect and are not depolarized in the presence of light, when the light is turned off the Off cell is stimulated and more glutamate is released. Off bipolars behave more like normal neurons, more glutamate makes them more depolarized.

diplopia

double vision, occurs when the retinal image in each eye is not integrated at the neuronal level and instead each image is processed individually, two percepts of one scene

circadian rhythms

drive our internal clocks, regulated by environmental light levels, small nucleus just above optic chasm to regulate this.

object motion

dynamic cue that arises when a moving thing is observed by a stationary observer

retinopy in LGN

each of the six layers is monocular in processing, 1,4, 6 process contralateral signals and 2,3,5 process ipsilateral signals

retinotopic layout of V1

each point on the retina is represented in a particular part of v1, fovea has more representation than periphery, density of ganglion cells in retina is much greater than periphery

eccentricity and motion

eccentricity affects motion and movement, central visual field has lower motion thresholds than periphery. retinal ganglion cells in peripheral retina have larger receptive fields.

interocular transfer

effect happens when you view two objects through two different eyes, MUST HAPPEN IN AREA V1 since before that only monocular neurons exist

plane polarized light

electric and magnetic fields restricted to only one plane, electric field oscillates in vertical place and magnetic only goes in horizontal direction.

horopter

empirical one is flatter than the theoretical one

nodal point

entire cone of rays emitted from a point source can be collapsed into a single ray passing the nodal point where all of the rays come to pass to be reflected on the opposite side of the retina.

Dark current

entry of sodium ions into the outer segment of photoreceptors (which are gated so that sodium can only flow in when cGMP binds to them). K+ flows out when Na+ flows in which keeps ionic charges stable, but eventually sodium potassium pump regulates sodium to be concentrated mainly outside.

R+/G- neurons

excited by red and inhibited by green

oculomotor response

eye movement response, most sensitive in terms of object tracking, direct relationship between response and object motion

myopia

eyeball is too long given the refractive power of the eye. parallel light is focused on a point that lies in front of the retina, greater divergence of light rays causes image point to be backwards (nearsightedness)

hyperopia

eyeball is too short in diameter, the retina lies ahead of where it should normally be. this causes far sightedness, less accommodative range for viewing closeby objects, more blur for things up close

VOR

fast and reflexive response that automatically occurs whenever we rotate our head

conjunctive eye movenemts

for object tracking and gaze shifts

photopigment

found in both rods and cones, captures light photons to generate electrical signals. Photopigment in all mammals is rhodopsin.

fovea vs. periphery

fovea = detaisl, periphery = changes in light detection

foveal region processes

fovea signals should be split down the middle exactly but this is highly unlikely, some go to contralateral side and some go to ipsilateral side of the brain.

range of vision

from the near point to optical infinity

area LIP and area FEF

frontal cortex, mechanisms for controlling eye movement functions including several areas in the parietal cortex.

spectrum

full range of electromagnetic radiation that can be produced by both natural and artificial sources.

white

fully reflects all colors

lens aberrations

further away one is from the optic axis the greater degradation in the image presented

figure ground segregration

gestalt explains why a foreground figure or impression stands out against a background.

phi movement

gestalt phenomenon when two lights flicker close by each other and it appears light is bouncing between them

aperture problem

global motion of an object through an aperture not a faithful representation of the actual movement of the object

glutamate and phototransduction

glutamate is the neurotransmitter produced by both rod and cone photoreceptors and it is excitatory, the next level of neurons has to interpret the fact that there is a decrease in glutamate and not an increase.

temporal contrast sensitivity function

greater temporal ability to resolve a particular frequency, lower contrast needed to observe a flicker optimally flickers around 10-15 hz range

color lights + color objects

greatly affects perception, things absorb different wavelengths so colored objects and lights are weird

orientation columns

half the width of the ocular dominance columns, neurons in each column are largely tuned to a specific bar orientation

polarization

happens under certain conditions

adaptation

happens with color afterimages, R/G neurons reach an adaptive stage where they become sluggish and stop responding to color stimulation

LGN structure

has six layers and serves as the main projection target of the optic tract even though it is one of the smaller neural structures it is critical to visual transmission and processing

retinal cells in periphery

have greater sensitivity but less resolution

aerial perspective

hazy quality of distant environmental objects caused by light scattering in the atmosphere

vergence eye movements

help to make sure that the objects that are fixated at different distances remain imaged exactly on the fovea

flicker perception

helps us understand this in more detail, visual stimulus used is normally a simple pattern presented in an alternting fashion with the goal of determining frequency

vestibular apparatus

helps with this, the balance organ located in the semi-circular canals of the ear, fluid in cochlea helps locate body in space

absolute absorption (rods)

highly sensitive in dim light conditions but they can only remain active for so long, beyond moderate light intensities rods cannot absorb any more photons and their photopigment becomes inactive

sclera

holds the eyeball together, similar in composition to the dura mater membrane in the brain, appears as the white part of the eye that shows in front

pupil

hole in the middle of the iris through which light can pas into the lens. changing size of it allows different amounts of light in

biological motion perception

how the visual system is able to extract a complex form from the movement a few points of light

Bezold Bunke effect

hue perception is affected by light intensity, increasing the intensity of colored lights causes the hue to shift in appearance to more yellow.

binocular vision (advantages)

if we lose one eye there is a second one there still

Dt > Dn

image is closer than the horopter, disparity exists in the retinal images

uncrossed disparity

image is further than the horopter, Dt < Dn, nasal image greater than temporal image, they are less crossed.

occlusion

image occlusion, when one object covers another object, we immediately know which is in front of the other

Hermann Grid

impression that there are spots at the intersection of various lines when there are none, when you look directly at the spot there is nothing there. the output is only of a few cells and the ganglion, different firing rates based on location cause us to believed there are spots where thre are none

prosopagnosia

inability to recognize faces, other visual functions are spared completely, FACIAL PERCEPTION IS DISTINCT FROM ALL OTHER FORMS OF PERCEPTION!

retinal magnification

increases rapidly as the image spreads over the entirety of the retina

bidirectional information flow

information flows in these areas and neural signals can do feedforward or feedbackward projections.

binocular vision

input from two eyes, not until 19th century true benefits of binocularity are understood

retina

inside the choroid, "film of the eye" refractive element that has an optical image superimposed into it by light from the outside world. made up of made layers of specialized neurons that transduce light nergy into neural signals

grating

inter-digitated set of light and dark bars, the width of these bars can be increased or decreased to provide a stimulus with different degrees of spatial detail and the intensity values of light and dark can be changed relative to each other to produce contrast

microsaccades

involuntary movements, these produce retinal stablization effects

color contrast

juxtaposition of two colors (such as yellow and blue), alters the perception of one object or another

parasol ganglion cells

large size and dendritic field, axons form the major output of the retina to separate parts of the visual pathway

LGN

lateral geniculate nucleus, the major thalamic structure that is the the principle subcortical target of the retinal projection, plays a critical role in transferring visual information to the occipital lobe.

medial and lateral

left and right, superior and inferior

bipolar cells

lie between photoreceptors and ganglion cells, main function is to transmit signals between the photoreceptors and ganglion cells

extrastriate areas

lie beyond V1, including V2, V3, V4... all the way up to 40. M and P distinctions are carried on after leaving V1.

photoreceptors

light absorbing elements of the retina, first events of vision occur here, light is absorbed to produce a neural signal

how is phototransduction done

light absorption leads to hyperpolarization, removal of cGMP by an enzyme means that there is less of it binding to sodium channels, making the channels shut down and preventing sodium ions from entering the cell. this stops the dark current.

point source

light coming from a single point, from this single point it spreads in all directions.

wave fronts

light going through a vacuum consisting of concentric circles that are very small in the immediate vicinity of the point source and then expand progressively as they radiate, eventually flattening out

reflection

light hits an object but it cannot create sufficient vibrational motion to create heat so it is reflected back into the environment instead

luminance (achromatic channel)

lightness information, color opponent neurons respond to COLOR info and On/Off neurons respond to this

metamers

lights/surfaces that are perceptually identified as identical but differ physically, can be produced by a trio of primaries, a specific hue doesn't need to be made of a unique physical spectrum.

nonspectral colors

like white, don't exist on their own, only exist as made up of other colors,

biological limits of resolution

limited by the packing density of the photoreceptor array, our eye is basically as good as it can get.

Panum's fusional area

limited range depth in front of and behind the horopter where objects are fused or single. single vision is possible in this range because disparity is within the range encompassed by the visual system (leads to stereoscopic depth perception)

directional selectivity

neurons show significantly greater firing to a stimulus moving in a given direction compared to all others, motion detecting neurons must happen becauseu the movement across the retina must be properly encoded to create an impression of movement

midline stereopsis

normal stereoscopic depth perception occurs for objects located along the midline

what is weird about visual system action potentials?

normally, hyperpolarization leads us to think inhibition but in this cause it is the opposite

color is metathetic

not quantitatively measured, cannot say 'this is more green'

size distance relationship

object distance increases, retinal image size is greatly reduced, as distance increases the retinal image decreases but not at a constant rate (much occurs around near point of vision)

first order motion

object motion defined by luminance is the most commonly occurring motion in the natural world

retinal image size and absolute depth

objected is fixed on the fovea and it can be moved forward or backward on the projection axis

accommodation

objects of different sizes make the crystalline lens and ciliary muscles change the refractive power of the lens, a clue to the brain about absolute depth

crossed disparity

objects situated closer than the horopter have D > 0 because they have a plus disparity

motion parallax

observer is moving but looking at stationary objects, a person on a train looking out the window

contrast sensitivity functions (CSF)

obtained using gratings, find the minimum conrtast threshold needed to make a grating of a particular spatial frequency just visible, repeated across multiple frequencies. Peak of these functions represents the optimal spatial frequency for human visual function

Mie scattering

occurs due to larger particles such as dust, smoke, water vapor. lower parts of the atmosphere, not dependent on wavelength.

early vision color processing

occurs in the retina with three different types of cones that can absorb light, following this, selective input from photoreceptors causes color opponency at the ganglion cell layer

second order motion

occurs more in conditions of isoluminance (underwater)

identity from motion

occurs very fast and is usually very accurate, ability to closely identify friends and family from far away

light scattering

occurs when light interacts with gaseous particles in the atmosphere, first light is absorbed by a particle and then it is re-emitted in a random direction. there are three types of it

Non selective scattering

occurs when particles are much larger than the wavelength of light, also wavelength independent and equally affects radiation from across the visible spectrum.

Rayleigh scattering

occurs when particles are of a small size compared to the wavelength of light, molecules like nitrogen and oxygen. Dominant form of scattering in the upper atmosphere. Short wavelengths scatter much more than longer wavelengths.

Functional architecture of V1

ocular dominance columns because any two neurons might differ in any of the categories

disjunctive eye movements

oculomotor responses in which eyes rotate in opposite directions, occur during either convergence or divergence

refractive power

of a lens, determined by how much refraction will occur at the two surfaces. things with bigger refractive indexes have higher refractive power.

fixational micromovements

of the eye, these are small and jittery movements that cause the image to shift slightly over the retina, essential for vision

On activation and bipolar cells

on center cell absorbs light and becomes hyperpolarized briefly before a drop in the release of glutamate, reduction in glutamate excites the bipolar cell (not normal response) which turns off depolarization

motion aftereffect

one must look at a moving object for a prolonged period after which a stationary object will move in a direction opposite from the other object

eccentricity

one to one ratio cannot be maintained outside the fovea so there is a great deal of eccentricity as you move from the fovea to the perihpery. greater eccentricity means more photoreceptors feeding into a ganglion cell

iris

opaque curtain like structure that is a forward extension of the pigmented layer of the choroid

ice cube model

orientation columns and ocular dominance columns run perpendicular to one another, each ocular dominance column contains orientation colums and everything is possible

particle theory

original way that people thought light traveled through space, could not account for diffraction

electromagnetic radiation

oscillating charged particles do this type of movement, a moving energy field that is found everywhere in nature . All of this is characterized by the flow of photons.

divergence

our eyes move from a close object to one that is further away, causes the opposite (less radical degrees)

subtractive color mixtures

paint, subtracts part of the reflective spectrum, wavelengths that remain are what we perceive as color.

superior colliculus

paired structure just below the LGN close to the midline of the brain.

stereopsis

part of binocular vision that endows us with amazing depth discrimination ability

fovea

part of the retina that divides the nasal and temporal halves. also where we focus on objects of interest for focusing in detail on images and for object scrutiny and details.

receptive field

part of the retina that influences a neuron by way of excitation or inhibition, each cell has a limited region of the retina.

astigmatism

partial blurring of the retinal image along the affected direction

nyctalopia

pathological condition of night blindess that causes photopic vision to dominate at wavelenths below 650 nm

Emmert's law

perceived size of an afterimage depends on projection distance

lambertian surface

perfectly matte surfaces, no reflection

choroid

peripheral rim of the eye, contains a rich blood supply and additional components contain pigmented layers of cells that provide nourishment to all cells in the immediate vicinity

early vision

phenomenon of the visual system that arise because of the way the retina is set up.

dual theory of light

photons are particles that travel in a wave, encompasses both parts of contrasting theories of what light is

photopic conditions

photopic has lower sensitivity and operates only under more intense conditions. Resolution much better since that's important for daytime vision.

computational load

photopic system has a greater one because of the high degree of image detail it must be capable of processing, fact that there are three types of cones in the eye shows this also.

division of labor

photopic system, arises from the central retina and detail and then the peripheral retina and color processing

monochromatic lights

physical characteristics to produce a highly saturated hue, lights that contain only one hue.

color space

physical distance map of how similar or dissimilar colors are, COLOR as we think of it is made of three things

image raster

point by point representation of the retinal image. begins with center surround detection carried out by retinal neurons, creates form primitives.

optic disk

point in the nasal retina through which retinal nerve fibers exit the eyeball, also known as the blind spot, no photoreceptors exist in the optic disk.

usefulness of CSF

portays the spatial capacities of visual processing by providing information on relative visibility gratings at different spatial freqencies.

measuring retinal image distance

position of any retinal image is measured by it's distance from the fovea

pop out phenomenon

pre-attentive elemental map proved by this, certain features pop out when they are different from 'distractors' in a photo (proves attention important in FIT)

midbrain and reflexes

pretectum and edinger-wesphal nucleus and two small collections of neurons that process specific aspects of visual information, if the light level in the retinal image is too high or low they alter the lens and pupil size

rod photoreceptors

produce the greatest signal around 500 nm light, it is hard to test only one type of receptor

optical imaging

produced maps that display areas of high neural activity in the visual cortex in response to being activated by a specific stimulus. brain areas that are more active reflect less light.

spectral sensitivity function

profiles the human visual system's senstivity to light at different wavelengths (reflect behavioral tendencies of humans)

dorsal and ventral streams

project from area V1, the area of the brain that is primarily concerned with visual processing, after leaving V1 visual information travels along one of these two paths.

two classes of neurons in V1

projection neurons and interneurons, projection neurons send information to other parts of the brain and are pyramidal in structure (excitatory) and interneurons are responsible for local connections and can be excitatory or inhibitory.

ventral cortical stream

projections of visual information leading to this area in the temporal lobe, what pathway and structure and composition

color opponency theory

proposed by Hering, idea that there are four color selective cells in the LGN that process color information in opponent manner

spectral relationships

quantitative aspects to do with the spectrum of visible light and their perceptual effects

emission spectrum

radiant energy emitted by the sun is restricted to a small range of the spectrum containing UV, infrared and visible bands of light.

depth of field

range of object distances that produces a sharp image, the smaller the aperture the greater the depth of field (more focus for smaller distances)

temporal frequency

rate of change of a stimulus, specified in terms of cycles of change per second.

tau

ratio of changing retinal image size of an approaching object - provides an accurate estimate of TTC

perspective projection

recaptures the third dimension, objects become smaller as they recede, must become smaller if this should faithfully represent distance in reality.

SC and visual input

receives a large visual input from the visual cortex that arrives into the superficial layers, somatosensory and auditory information also project to the SC

structure from motion

recovery of three dimensional information and its use in producing form perception

ROYGIBV

red, orange, yellow, green, indigo, blue, violet (from longest to shortest wavelength)

visual egocenter

reference point on the body for judging the directions of objects, the midpoint between the two eyes is the cyclopean eye

refractive index

refers to the speed of light through a medium, the greater the refractive index the slower the speed of light within it

specular reflection

reflection at the surface of an object, simple mirror like reflection that affects all wavelenghts of incident light in equal manners

aqueous humour

region immediately behind the cornea contains this liquid

photopic vision

regulated by the three types of cones, day vision

brightness

related to the physical parameter of intensity

inverse square law

relationship to light and observation, if you increase distance by three you must reduce light by nine. the outward moving sphere idea

relative size

relative size of objects makes things appear bigger or smaller depending on where they are in the picture

HSV color space

represented as a prism (either cone or cylinder) that shows all combinations of HSV

body reflection

responsible for giving an object it's color, objects reflecting all lights look white to us, takes on a specific color when it reflects unequal amounts of light

bistratified ganglion cells

responsible for yellow and blue information

correspondence problem

retina transmits mosaics of point by point light to the LGN and then to area V1, how is the set of points identified in one image with the same set in another?

large vs small pupils and blurring

retinal blurring is greatest with large pupils and small with smaller pupils, two objects at different depth plans will be at their sharpest when the pupils are small

feedback connections

reverse, as well as undirectional neurons. various higher visual areas are interconnected with forward and reverse lines of communication

spectrophotometry

rhodopsin molecules are collected and then released with other molecules, shine light into rhodopsin to see what the light that is not absorbed is.

lowest threshold detection

rod photoreceptors can respons to a single photon under ideal conditions

rod vision and color

rod vision is color blind, the intensity of a light must reach cone activation threshold in order for color to be determined.

extraocular muscles

rotation in the orbital socket allows a lot of precision, but there are six of these that are tightly packed in

protein in the sclera

sclera has protein fibers arranged in an irregular pattern so that light is reflected and scattered, this changes as the sclera moves to the front where it is highly parallel

scotopic conditions

scotopic is very sensitive system and only functions under dim light conditions. resolution not as good since that isn't necessary in these conditions

melatonin

secreted by pineal gland, exerts influence for the onset of sleep, inhibited by light.

photochromatic interval

sensitivity difference between just seeing a light (scotopic vision) and just being able to tell the color (photopic vision) this interval between the two functions is greatest at low wavelengths and decreases at longer ones.

coronal plane

separates front and back of the body, Y axis, movement around pitch

crystalline lens

separates the two liquids, the lens or second refractive center in the eye. ligaments and muscles hold it in place, transparent to allow rays to pass through it.

correspondence problems

sequences of events don't match what's actually happening, space important factor

purkinje tree

shadow cast on photoreceptor array by the network of blood vessels present in each eye

resolution in the eye

sharp increase in the fovea and gradual decrease as things move to the periphery.

lightness constancy

shifts in the environment don't cause perceptive shifts because we have objects and their surroundings equally affected by the change in equal amounts.

S-cone

short wavelength cones, absorb best around 440 nm

absorption spectrum

shows how much light is absorbed by rod photopigment across the entire visible spectrum. absorption is not constant across all wavelengths

law of similarity

similar items are grouped together since they share common features in terms of shape, size, orientation, color or lightness

OKN

similar reaction, eyes snap from object to object

trichromatic theory

since there are three pieces of light that cannot be broken down and they produce all colors we see, there are three detectors (thomas young, physicist)

photons

small particles that light travels in that have a wave like quality associated with them, energy is concentrated and it is believed they travel in a wave through space

intersection of constraints

solves the problem, true motion of the object is derived from the one motion vector constant across all parts

motion

spationtemporal events, object moves a certain amount of space in a certain amount of time

peripheral retina

specialized for detection of low light, has most light sensitive part of the eye because it is dedicated to night vision, more rods here.

chromaticity

spectral characteristics of light and the reflective nature of objects, physical and psychological aspects that contribute to color vision.

transmission spectrum

spectrum of light from the sun transmitted to earth through the atmosphere, life on earth uses most of this as it's visible spectrum light.

velocity

speed and direction

eyeball

spherical structure about one inch in diameter

Bloch's law

stimulation time and intensity must be traded off, the product of light intensity and duration must reach a critical value to produce detection. beyond an upper limit there is no additional value to having the twocombined in a critical manner

apparent motion

stimulus presented at one location and then shown at another shortly afterward, produces a vivid impression of movement that cannot be distinguished from actual motion

correlated dot motion

stimulus useful in both physiological and psychophysical studies, each dot moves in a random direction which causes visual dynamic noise. we see random dot movements and there is no coherent movement in a direction that stands out.

stereopsis (detail)

subtle differences in the retinal images in each eye endow us with the ability to create the third dimension, this is why depth perception occurs in binocular viewing conditions

mach bands

tendency to see dark and light bands at boundaries where the lightness changes abruptly (even though the color is constant) false impression of a narrow dark/light band immediately to the left or right of each boundary.

geons

the 3d volumes that are assembled into many small and common objects,

integrative role

the SC has a highly integrative role in perceptual processing, touch sound and sight informaton

color vision

the ability to discriminate different lights based on their wavelength contents (significant survival and reprocutive advantages)

hue

the chromatic quality of a color, three different physical spectra produce three different hues (700 nm, 500 nm, and 400 nm for example)

retinal disparity

the difference in the location of the binocular images, defined by the letter D.

optic flow and retinal image

the expansion and looming that occurs when there is a large or small amount of peripheral movement

functional anatomy

the functional aspects of cortical architecture and how they are related to one another, able to expand the field because of new brain imaging techniques

nyquist limit

the highest possible spatial frequency that can be theoretically sampled, determined by the spacing of the photoreceptor array. For the fovea, based on center to center spacing of receptors is 60 cycles per degree

color constancy

the idea that colored surfaces appear relatively unchanged even when there are lighting changes because otherwise vision would not make sense

retinex theory

the idea that the eye (retina) and the brain (cortex) are both involved in color constancy processing, derived through experiments with mondrians.

face perception

the most complex objects that we can possibly recognize and retain information about

heuristics

the most plausible solution to a problem given the circumstances taking place around the problem. Gestalt principles are heuristics and not laws.

nystagmus

the name for this type of sequence (spinning in circles) fluid in VOR keeps spinning when you stop

mesopic vision

the narrow light range over which both can operate, but even here they function independently of each other.

red, green and blue

the only three colors than cannot be broken down into other colors (when talking about light)

retinal ganglion cells

the output neurons in the retina that carry signal from the eye to the brain, axons leave the retina to the brain. action potentials are generated here

how do mach bands arise?

the output of a select group of retinal ganglion cells, there is a large stimulus that casts an image on a lot of ganglion cells. since they are On/Off, the two cells have the same output but the relative difference is repeated among ganglion cells.

Fusiform face area (FFA)

the part of the fusiform gyrus that is specified for processing facial stimuli. human faces have great variation but still facial perception is completely holistic in nature (object is feature by feature then integrated after)

geniculocortical pathway

the projections from the LGN to the visual cortex, much more dominant than the SC

nocturnal bottleneck

the reason we developed color vision probably has to do with the transition of humans to daylight conditions

optic flow

the relative movement of different parts of a visual scene that occurs during self-motion

corresponding retinal images

the representations on the retinae is not exactly the same, they correspond more than they mirror (temporal and nasal halves of the retina)

duplex processing

the retina is a duplex processor, meaning that it has rods optimally functioning in dim light and cones optimally in daylight

dorsal cortical stream

the signal output from MT goes to the areas of the parietal lobe that make this up, the where pathway and spatial relationships to objects

optic chasm

the two optic nerves come together and then separate here, at this point nasal and temporal signals separate and follow different routes. temporal half projects to the same side and the nasal half crosses over to the opposite LGN

size of visual field with binocular vision

the visual field size is larger with binocular vision, two eyes have the largest field size because they are front placed

shape from shading

the way light is reflected off curved surfaces, depends on the shading quality a lot for information

schematic eye

theoretical concept that takes into account optical properties of the cornea and lens to arrive at details of image location and quality. cornea, lens, and retina are the key parts.

vieth muller circle

theoretical horopter, where everything produces optical images at analogous points on the eyes.

grandmother neurons

there are single neurons in the temporal lobe that are responsible for coding visual representation at the most complex levels.

functional segregation

there are two ganglion cell types in the retina (Midget and Parasol) and this is retained in layers of the LGN where parasol cells project to layers 1 and 2.

similarities in cones

they all have the same profile, but slightly displaced in order to account for all light

Midget and parasol cells

they have different field sizes and receptive fields and they set the stage for two distinct and separate pathways to the brain

LGN neurons receptive fields

they have receptive fields organized in a similar fashion to ganglion cells receptive fields, concentric circular representation with and On center and Off surround (or vice versa)

Layer 4 (v1)

thickest layer of area V1, dived into sets of sublayers 4a, 4b, 4c.

image blur

things in the foreground or background of something cause the retina to be adjusted to look at those objects, further away or closer up objects

texture gradient

things that are closer are rougher, things that are further away are smoother

allocentric

this is the frame of reference that is defined in an external manner

layers of retinal neurons

three layers discovered by Stephen Polyak, photoreceptors outermost, inner nuclear layer in the middle of the segment, ganglion cell layer along inside margin of the retina

transverse plane

top and bottom half, movement around known as roll, X axis

retinotopic organization

topographic layout of the retina is formed in each of the layers of the LGN, adjacent points in the retina are mapped onto adjacent points in layers of the LGN.

smooth pursuit

tracking a moving object by shifting gaze

color afterimage

transient afterimage or impression of opposite colors than the ones that were there.

purkinje shift

transition in sensitivity from scotopic to photopic vision between 500 and 550 nm, accompanied by a brighter sensation for light intensities at lower wavelengths (colors with lower wavelengths like green appear brighter because the scotopic system is more sensitive at those wavelengths)

layers 2 and 3 (v1)

transmit information to other visual cortical areas (temporal and parietal lobes for example)

layers 5 and 6 (V1)

transmit information to subcortical structures such as the LGN and SC.

cornea

transparent fron part of the eye which is the first of two refractive elements in the eye

binocular suppression and integration

twin processes that give rise to the singleness of vision that fuse objects within a given range and ensures we see only a single object

binocular rivalry

two images that inhibit each other, creates an oscillation effect so the two orientations are never processed simultaneously.

cyclopean perception

unified single view of the world arises from having two eyes

kinetic depth

used to refer to the motion cues generated by the movement of objects in different depth planes (closer objects often appear to have moved more than further away ones)

sensitivity and resolution

usually conditions in which sensitivity is increased lead to lower resolution and vice versa

yellow's saturating power

very low, need a lot of it to make white light appear yellow

egocentric

viewer centric frame of reference points, object positions are specified in this way. What humans do

ocular cues

visual clues that help us realize what our absolute depth is in space

binocular summation

visual detection with both eyes superior to that of either eye alone, especially under low lighting conditions

scotopic vision

visual processes mediated only by rod photoreceptors, dim lighting settings

feature integration theory (FIT)

visual processing begins with the capture of elemental features across the retinotopic map and these form a feature map, earliest thing the visual system can work with

acuity

visual resolution or the ability to detect fine details in an optical image.

saccadic suppression

visual sensitivity during a saccade is reduced through neurobiological mechanisms so that we don't go blind during the saccade.

random dot stereograms

visual system extracts disparity information by making a point by point match of the two retinal images, random dot stereograms do not have shape information

Time to collision (TTC)

visual system needs to evaluate depth of an object as well as it's trajectory and the speed of approach to determine what the time to collision is

moon illusion

vivid appearance of a large moon on the horizon compared to the zenith, happens because we assume horizon is further away than sky above

maximum efficiency

we are most efficient at detecting constast more than any other aspect of light.

binding problem

we can only bind things in the right way (assemble tokens into a visual object) when we focus our attention on an object

color discrimination ability

we have good ability to discern and discriminate between different types of color information, trichromatic visual system is capable of producing a vast number of perceived hues ( <2nm change in wavelength needed to detect hue change)

nanometers

we measure wavelength in this to account for the various variation among types of light

refraction

what lenses use to transmit signals, refers to the bending of light that occurs when it changes medium that it travels through

wagonwheel effect

wheels moving fast enough appear to rotate backwards because our brain simply sees them that way since it is easier for it

absorption

when light hits an object and the atoms can turn the energy into heat the light is absorbed and turned into vibrational motion that subsequently turns into heat.

convergence

when our eyes move from a far away object to a closer one, the eyes have to roll in more so that the right is turning counter clockwise and left clockwise

Dt = Dn

when the images in corresponding retinal images are all identically displaced from the fovea, true for any images on the the horopter. Any pair of corresponding retinal images is defined by the fact that Dt=Dn.

optical infinity

when the wave fronts are flat.

LGN neurons and attention

when we are attending more to a stimulus (focusing on details) there is increased firing in LGN neurons

white in color circle

white is in the middle of the color circle, when you mix any two colors directly opposite each other you get white.

Abney effect

white light tends to be more violet than red so you have to add more red to it to make it white.

gestalt psychology

whole is different frm the sum of it's parts, wholeness of structure, object shouldn't be broken down into parts because they won't mean anything to observers

Rods

Better at night vision, have a slender appearance and are far more numerous in the eye.

emmetropia

"perfect" eye, parallel incident rays are imaged exactly on the retina, must be perfectly focused on the retina in order to be an emmetropic eye

spectral range ( human vision)

400-700 nm, intensity and wavelength determine how much light is absorbed by photoreceptors

what wavelength is most efficient at absorbing

500 nm (bluish green light)

striate cortex

AKA primary visual cortex, occipital lobe at the back of the brain, processing in visual information takes a jump in complexity here. there are 17 of brodmann's areas

Dt- DN

Distance of temporal side minus distance of nasal side of the retina

difference between channels and streams

M and P are channels that are anatomically segregated and functionally divided. Channels give way to streams in higher vision

raw primal sketch

MIT, visual system uses edge detection to create spatial primitives composed of edges, lines and blobs.

rhodopsin bleaching (cones)

MUCH higher activation threshold, only become completely bleached under really extreme lighting conditions such as looking at the sun

On/Off

On center means that the center of the receptive field will fire when light falls on it, an excitatory response

vestibulo-ocular reflex

VOR reflex generated, vestibular apparatus, receptor cells in this organ register self motion along different planes and transmit neural impulses accordingly.

light ray

a better representation of traveling light, straight line path taken by a photon

directional tuning curve

a circular profile, neuron responds well regardless of what direction a light bar is moving, fire equally well to all directions of stimulus movement

circuitry of cone photoreceptors and ganglion cells

a cone is connected to two different bipolar cells, an off and on one.

chromatic appearance of objects

a mix of the reflectance properties of the object as well as the wavelength content in the incidence light.

hypercolumn

a pair of ocular dominance columns in conjunction with one series of orientation columns, a discrete module. a portion of the cortex where all visual functions are possible for a very small part of the retinal field

reflectance spectrum

a plot of the amount of reflection as a function of wavelength. all objects have spikes at different points in the spectrum, why objects have colors

Center surround antagonism

a property of ganglion cells because of their concentric opposing excitation profiles, oppose each other interms of firing of ganglion cells. makes the retinal output of ganglion cells driven primarily by light contrast

isoluminance

luminance is constant across the stimulus and the background and only the color varies, leading to differences in hue only (not saturation or brightness)

color circle

made by newton, the first graphic model of color perception, paved the way for current procedures where any intermediate color can be predicted from the mixture of two colored lights.

human eye

made up of peripheral components which are the outer parts of the eye as well as interior components

area V1 structure

made up of six layers, layer 1 at the top and layer 6 at the bottom. layers differ in density of neurons, cell dense layers are in between less dense layers

trichromatic detector system (T)

made up of three detectors for short wavelengths, violet, medium wavelengths, green, and long wavelengths, red. Known respectively as S, M, and L detectors.

Sulcus Colliculus and movement

main role is integration, output to areas on the brainstem that control saccades

photoreceptor membrane voltage

maintained by sodium channels flowing in and potassium flowing out to be maintained at around -40 mv.

photopic -> scotopic effect on color

makes green hues appear brighter and yellows appear dimmer, purkinje shift.

Off/On

means that it will be inhibited when light falls onto it and has excitation zones around it.

microelectrodes

measure output of the retinal ganglion cells, amplified and displayed on a device to capture the number of action potentials generated over a period of time

M cone

medium cones, absorb best around 530 nm

explanation of metameric mixtures

metameric mixtures occur because colors have the same trichromatic activation profile (our brain only reads the output, cannot decipher exactly what goes in)

increment threshold

minimum contrast needed for a light spot to be detected against a dark background.

Ponzo Illusion

misconceptions of relative distance, two lines appear different sizes in a receding image

visual system

most dominant sensory system, provides enormous evolutionary benefits, nearly half the brain is devoted to visual sensation

unpolarized light

most light, contains many directions and not as exact as polarized

rectus muscles

move eyes along vertical and horizontal axes, symmetric around the eyeball to each other

proprioception

movement and detection of our bodies in space, usually is accompanied by some form of corollary discharge, efference copy sent to sensory systems that helps account for the movement.

kinetic depth effect

movement can enhance the three dimensional appearance of objects in space, ability to construct the three dimensional structure of complex objects from motion signals alone

vection illusion

movement of a vehicle outside leads too an illusion we are moving opposite it

induced motion

movement of one object makes it appear as if another is moving

vitreous humour

much larger area right in front of the reina, clear liquids that exert outwards pressure on the eye so it stays spherical

properties of medium that light travels in

must be transparent otherwise light will not be transmitted

near point

natural limit in the process of accommodation, the limited extent to which the lens can be rounded. Objects placed any closer will appear blurred.

orientation tuning curve

neuron's response profile and action potential firing rate can be plotted in terms of the light bar's orientation, there is a symmetric decline in the firing rate as the orientation becomes too different from the neuron for a stimulus to be detected

Parvocellular layers of the LGN

neurons in the four top layers that have smaller cell bodies.

Magnocellular layers of the Lgn

neurons in the lowest two layers that have large cell bodies