Sensation and Perception (Chapter 4)

Ponzo illusion

Converging lines enclose two objects of identical size, leading us to perceive the object closer to the converging lines as larger; our brain assumes that the object closer to the converging lines is farther away, and compensates by making the object look bigger

Cultural effects on perception

Culture that doesn't have straight lines...?

Sensory adaptation

A decline in activation within a sense receptor after initial activation

Muller-Lyer illusion

A line of identical length appears longer when it ends in a set of arrowheads pointing inward than in a set of arrowheads pointing outward; because we perceive lines as part of a larger context

Perceptual set

A mental predisposition to perceive one thing and not another; usually based on experience; the influence that expectations have on perception

Depth perception: binocular and monocular cues (from both lecture and book)

Ability to see spatial relations in three dimensions; we use two kinds of cues to gauge depth Monocular depth cues: stimuli that enable us to judge depth using only one eye Relative size: more distant objects look smaller than closer objects Texture gradient: texture of objects becomes less apparent as objects move farther away Interposition: one object that's closer blocks our view of an object behind it Linear perspective: the outlines of rooms or buildings converge as distance increases Light and shadow: objects cast shadows that give us a sense of their three-dimensional form Motion parallax: nearby objects seem to move faster than those far away because near objects move across the retina more quickly Binocular depth cues: stimuli that enable us to judge depth using both eyes Binocular disparity: our left and right eyes transmit quite different information for near objects but see distant objects similarly, and our brains make use of this to judge depth Binocular convergence: when we look at nearby objects, we reflexively focus on them by using our eye muscles to turn our eyes inward and our brain uses how much our eyes are converging to estimate distance

What the following optical illusions look like and why they arise

Afterimage illusions, Peripheral drift illusion, Reversible figure illusion, "Impossible doghouse" illusion, Shadow illusion, Illusory contours, Ponzo illusion, Ames Room illusion, Muller-Lyer illusion

Reversible figure illusion

Ambiguous images or reversible figures are optical illusion images which exploit graphical similarities and other properties of visual system interpretation between two or more distinct image forms. These are famous for inducing the phenomenon of multistable perception. Multistable perception is the occurrence of an image being able to provide multiple, although stable, perceptions. Classic examples of this are the rabbit/duck and the Rubin vase. Ambiguous images are important to the field of psychology because they are often research tools used in experiments.

Ames Room illusion

An Ames room is a distorted room that is used to create an optical illusion. An Ames room is viewed with one eye through a pinhole such as to avoid any clues from stereopsis, and it is constructed so that from the front it appears to be an ordinary cubic-shaped room, with a back wall and two side walls parallel to each other and perpendicular to the horizontally level floor and ceiling. However, this is a trick of perspective and the true shape of the room is trapezoidal: the walls are slanted and the ceiling and floor are at an incline, and the right corner is much closer to the front-positioned observer than the left corner (or vice versa). As a result of the optical illusion, a person standing in one corner appears to the observer to be a giant, while a person standing in the other corner appears to be a dwarf. The illusion is so convincing that a person walking back and forth from the left corner to the right corner appears to grow or shrink.

Cochlea

Bony, spiral-shaped sense organ used for hearing, converts vibration into neural activity

Afterimage illusions

Caused by opponent processes; occur when the chemicals in the "on" neurons for a certain color get depleted; bottom-up

Opponent-process system

Cells further back in visual system are turned on by one color and off by its opponent Blue-yellow Red-green Black-white Opponent-processes cause afterimage illusions; they occur when the chemicals in the on neurons for a certain color get depleted; bottom-up

Synesthesia

Condition in which people experience cross-modal sensations, like hearing sounds when they see colors; may be an extreme version of cross-modal responses that most of us experience

Trichromatic system

Cones are specialized to respond to red, blue, or green light

Photoreceptors - types and specialization

Cones: color, detail Rods: brightness, movement

Gestalt psychology

Demonstrates that a figure forms a "whole" which is qualitatively different than the sum of its parts; help explain why we see much of our world as unified figures or forms rather than as a confusing jumble of lines and curves; top-down

Locating sound direction

Depends upon the time at which sound waves reach each ear. Straight ahead or behind = 0 microsecond difference. From right or left = 700 microsecond difference.

Hair cells

Ducts in the cochlea contain hair cells, our auditory receptors. Each hair cell has tiny hairs called cilia which protrude into the duct. When vibrations move membranes inside the cochlea, the hairs bend; cells translate the bending sensation into action potentials.

Why ESP is a weak theory

Extrasensory perception: perception of events outside the known channels of sensation Types: Precognition: predicting specific events before they occur through paranormal means Telepathy: reading other peoples' minds Clairvoyance: detecting the presence of objects or people that are hidden from view Evidence: Cards with different shapes, asked to guess which card would appear (precognition), which card another subject had in mind (telepathy), and which card was hidden from view (clairvoyance), 7 out of 25, where 5 is chance performance, but scientists couldn't replicate Research suggested that people could mentally transmit images to dreaming subjects, but scientists couldn't replicate results

The binding problem (and best way to explain it)

How our brain takes multiple pieces of information and combines them to represent something concrete, like an apple; our minds seamlessly combine shape, motion, color, depth cues into a single unified perception of a scene

Phi phenomenon

Illusory perception of movement produced by the successive flashing of images, like the flashing lights that seem to circle around a movie marquee; these lights are actually jumping from one spot on the marquee to another, but they appear continuous; show that our perceptions of what's moving and what's not are based on only partial information, with our brains making guesses about what's missing

Colorblindness

Inability to see some or all colors; due to the absence or reduced number of one or more types of cones stemming from genetic abnormalities; usually missing red or green cones

Lateral inhibition

Lateral inhibition occurs when the activity of one cell suppresses the activity of a nearby cell. In psychology, lateral inhibition illustrates that vision is not a passive process of seeing merely what is objectively there; it also explains optical illusions, notably Mach bands. Different photoreceptors in the eye respond to varying degrees of light. When one cell activates in response to light, its activity impairs or prevents neighboring cells from activating. This causes the edges between light and dark areas to appear more prominent than they would be otherwise. For example, without lateral inhibition, the border between a black tile and a while tile would appear less obvious.

Feature detection cells

Nerve cells in the visual cortex respond to specific features, such as edges, angles, and movement

Absolute threshold

Lowest level of a stimulus needed for the nervous system to detect a stimulus 50 percent of the time

Peripheral drift illusion

Occurs because information about bright colors travels through cells in the visual system faster than information about dark colors; organizing neurons mistakenly process this as movement; organizing neurons process big time gaps as movement from left to right; overall effect is illusion of left-right movement; bottom-up; blue and green circles with black dot in center

Consolidation of information in the visual system

Optic nerves connect to the thalamus in the middle of the brain, and the thalamus connects to the visual cortex.

Illusory contours

Our brains often provide missing information to help us make sense of a stimulus. The Kanizsa Square illustrates subjective contours. A mere hint of four corners can give rise to the perception of an imaginary square.

Law of complementarity

Pairs of colors which, when combined, cancel each other out are complementary. They produce black in subtractive color mixing (pigment), and white in additive color mixing (colored light).

Critical/sensitive periods - definition and evidence

Period in infancy or early childhood; sensory input from environment is necessary to organize brain areas which interpret biologically-prepared sensory abilities Examples: Cataracts since birth which are removed after childhood; visual ability will always be limited Cataracts which develop after early childhood; once removed, people restore complete vision American babies can recognize certain consonants that American adults can no longer sense (auditory system)

Rhodopsin

Pigment-containing sensory protein that converts light into an electrical signal; required for vision in dim light; located within retina's rod cells

Fovea

Point of central focus; responsible for acuity, or sharpness of vision

Subliminal perception

Processing of sensory information that occurs below the level of conscious awareness Evidence: when investigators subliminally trigger emotions by exposing subjects to words related to anger, these subjects are more likely to rate other people as hostile Subliminal information doesn't necessarily influence our product choices, votes, and life decisions because we can't engage in much, if any, in-depth processing of the meaning of subliminal stimuli

Gestalt principles of form perception

Proximity: objects close to each other tend to be perceived as unified wholes such as columns of lines Closure: when partial visual information is present, the mind fills in what's missing to create a coherent whole Figure-ground: we make an instant decision to focus attention on what we believe to be the central figure and largely ignore what we believe to be the background; if we look again, we can see an image in the background; vase or face Similarity: we group items based on their similar appearance; we perceive dots as forming 6 horizontal lines rather than 6 vertical lines because color Continuity: leads us to perceive the cross as one long vertical line crossing over one long horizontal line rather than 4 smaller line segments joined together Symmetry: two symmetrical figures tend to be grouped together as a single unit

Sensation vs. perception - how are they different?

Sensation: detection of physical energy by sense organs, which then send information to the brain Perception: the brain's interpretation of raw sensory inputs Sensation allows us to pick up the signals in our environments, and perception allows us to assemble these signals into something meaningful

Properties of sensory systems

Sensory adaptation, change, absolute threshold, difference threshold (JND), Weber's law

Change

Sensory systems respond to changes more readily than to steady states

Blind spot

Spot where optic nerve connects to retina; has no photoreceptors; part of the visual field we can't see; our visual cortex usually fills in missing information based on surrounding context

Vision

Stimulus: light waves Location: retina

Proprioception

Stimulus: location and movement of body parts Location: skin, joints, tendons, bones

Taste

Stimulus: molecules in food Location: taste buds

Smell

Stimulus: molecules in the air Location: olfactory receptors which connect to olfactory bulb

Balance

Stimulus: movement of ear fluid Location: semicircular canals

Touch/pain/temperature

Stimulus: pressure and other stimuli Location: skin and other tissues

Hearing

Stimulus: sound waves Location: cochlea

Perceptions of flavor

Sweet, sour, salty, bitter, umami (savory)

Perception - brain areas

Taste area between frontal and temporal lobe Somatosensory area between frontal lobe and parietal lobe Olfactory area between frontal lobe and temporal lobe Proprioception area in cerebellum Auditory area in temporal lobe Visual area in occipital lobe

Difference threshold (JND)

The minimum difference in intensity that is required for a person to perceive two stimuli as different

Transduction

The process by which the nervous system converts an external energy or a substance into excitation or inhibition of neurons in the brain; Example: specialized cells at the back of the eye transduce light and cells in a spiral-shaped organ in the ear transduce sound

Perceptual constancy

The process by which we perceive stimuli consistently across varied conditions Types: shape, size, color consistency

Weber's law

The size of the difference threshold depends on the magnitude of the original stimulus

Psychophysics

The study of how we perceive sensory stimuli based on their physical characteristics; Example: absolute threshold, just noticeable difference, signal-to-noise ratio

Location of the retina in the eye; location of photoreceptors on retina

Thin membrane at the back of the eye Rods: periphery; enable us to see basic shapes and forms; we rely on rods in low levels of light; no rods in the fovea, so we rely more on our peripheral vision at night; rods detect light, not color Cones: center; give color vision; require more light than rods do; faster to adapt to light changes, which is why we go through a period of dark adaptation

Top-down vs. bottom-up perception

Top-down: guided by higher-level processes, experience and expectations influence our interpretation of sensory information Bottom-up: analysis of the stimulus begins with the sense receptors and works up through more and more sophisticated processing areas in the brain Both types work together to create perception

The two systems that contribute to how we sense color

Trichromatic system, opponent-process system

Sensory systems: stimuli and locations

Vision, smell, taste, balance, hearing, touch/pain/temperature, proprioception

Perceptual adaptation - definition and evidence

We are adaptable to new sensory experiences Example: Vision distortion goggles

Shadow illusion

We unconsciously process shadowing cues in our environment so that things don't look like they're constantly changing color

Three-primaries law

We're sensitive to three primary colors of light: red, green, and blue. The mixing of varying amounts of these three primary colors (additive color mixing) can produce any color. Mixing equal amounts of red, green, and blue light produces white light.

Dark adaptation curves

When our ability to make things out in the dark gradually improves; due to rods being slower to adapt to light changes than cones