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the process by which our sensory receptors and nervous system receive and represent stimulus energies from our environment.


the process of organizing and interpreting sensory information; enabling us to recognize meaningful objects and events.

Bottom-up processing

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

Top-down processing

information processing guided by higher-level mental process, as when we construct perceptions drawing out our experience and expectation.


the study of relationship between the physical characteristic of stimuli, such as their intensity, and our psychological experience of them.

Absolute threshold

the minimum stimulation needed to detect a particular stimulus 50 percent of the time.

Signal detection theory

a theory predicting how and when we detect the presence of a faint stimuli ("signal") amid background stimulation ("noise"). Assume that there is no single absolute threshold and that focuses more on the processing of briefly stored information. (e.g. what determines a "hit", "miss," "false alarm" or "correct rejection")

Difference threshold

the minimum difference between two stimuli required for detection 50 percent of the time. We experience the difference threshold as a just noticeable difference (also called just noticeable difference or JND.)

Subliminal Sensation

detection of stimuli below absolute threshold

Weber's law

the principle that, to be perceived as different, two stimuli must differ by a constant minimum percentage (rather than a constant amount).

Sensory Adaptation

diminished sensitivity as a consequence of constant stimulation.


conversion of one form of energy into another. In sensation, the transforming of stimulus energies into neural impulses.


the distance from the peak of one light or sound wave to the peak of the next. Electromagnetic wavelengths vary from the short blips of cosmic rays to the long pulses of radio transmission.


height of a wave; influences brightness in visual perception and volume in audition


the dimension of color that is determine by the wavelength of light; what we know as the color names blue, green, and so forth.


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


a ring of muscle tissue that forms the color portions of the eye around the pupil and controls the size of the pupil opening.


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


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


the sharpness of vision.


a condition in which nearby objects are seen more clearly than distant objects because distant objects focus right in front of the retina.


the condition in which faraway objects are seen more clearly that near objects because the image of near objects is focused behind the retina.


retinal receptors that detect black, white, and gray; necessary for peripheral and twilight vision, when cones don't respond.


receptors cells that are concentrated near the center of the retina and that function in daylight or in well-lit conditions. The cones detect fine details and give rise to color sensation.

Optic nerve

the nerve that carries neural impulses from the eye to the brain.

Blind spot

the point at which the optic nerve leaves the eye; no receptors cells are located there. Creates a gap in our vision that is "filled" by the brain.


the central focal point in the retina, around which the eye's cones cluster.

Feature detectors

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

Parallel processing

the processing of several aspects of a problem simultaneously; the brain's natural mode of information processing for many functions, including vision. Contrast with the step-by-step (serial) processing of most computers and of conscious problem solving.

Young-Helmholtz Trichromatic theory

the theory that the retina contains three different colors receptors-one most sensitive to red, one to green, one to blue-which when stimulated in combination can produce the perception of any color.

Opponent-Process theory

the theory that opposing retinal processes (red-green, yellow-blue, white-black) enable color vision; useful for explaining the phenomenon of "after-images"

Color constancy

perceiving familiar objects as having consistent color, even if changing illumination alters the wavelengths reflected by the objects.


the sense of hearing


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


sound information that depends on frequency (or wavelength) of sound waves

Middle ear

the chamber between the eardrum and cochlea containing three tiny bones (hammer, anvil, and stirrup) that concentrate the vibrations of the eardrum on the cochlea's oval window.

Inner ear

the innermost part of the ear, containing the cochlea, semicircular canals, and vestibular sacs.


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

Place Theory

in hearing, the theory that links the pitch we hear with the place where the cochlea's membrane is stimulated.

Frequency theory

in hearing, the theory that the rate of nerve impulses traveling up the auditory nerve matches the frequency of a tone, thus enabling us to sense its pitch.

Conduction Hearing Loss

hearing loss caused by damage to the mechanical system that conducts sound waves to the cochlea.

Sensorineural hearing loss

hearing loss caused by damage to the cochlea's receptors cells or to the auditory nerves; also called nerve deafness.

Gate-Control theory

the theory that the spinal cord contains neurological "gate" that blocks pain signals or allows them to pass on to the brain. The "gate" is open by the activity of pain signals traveling up small nerve fibers and is closed by activity in larger fibers or by information coming form the brain.

Sensory interaction

the principle that one sense may influence another, as when the smell of food influences the taste.


the system for sensing the position and movement of individual body parts; enabled by feedback from proprioceptors (which provide info about the movement of muscles, tendons, joints)

Vestibular sense

the sense of body movement and position, including the sense of balance; enabled by feedback from semicircular canals in inner ear

hair cells

finger-like projections on the basilar membrane that stimulate activity of the auditory nerve


snail-shaped tube in the inner ear that contains fluid that moves in response to vibrations, stimulating activity on the basilar membrane

basilar membrane

area within the cochlea where hair cells are located

semicircular canals

fluid filled tubes in inner ear that provide information about movement of the head

Ernst Weber

early psychologist who established that the proportion of difference (rather than absolute difference) between two stimuli that is required for distinguishing between them is constant for particular types of sensation (e.g. weight, brightness, etc).

Gustav Fechner

often credited with founding "psychophysics" as a subfield of psychology

David Hubel & Torsten Wiesel

Nobel-prize-winning researchers who discovered "feature detectors" within the brain

cochlear implant

a device for converting sounds into electrical signals and stimulating the auditory nerve through electrodes threaded into the cochlea

sensory interaction

the principle that one sense may influence another, as when the smell of food influences taste


when one sort of sensation (such as hearing a sound) produces another (such as seeing color)


sense of smell


inability to recognize or perceive faces


a perceptual whole; derived from German word meaning "form" or "whole"


literally, "below threshold"; stimuli too weak to be consistently detected

selective attention

ability to attend to only a limited amount of sensory information at one time

cocktail party effect

ability to selectively attend to one voice among many


A gestalt perceptual phenomenon; the organization of the visual field into objects that stand out from their surroundings


the perceptual tendency to organize stimuli into coherent groups


Gestalt grouping principle; we group nearby figures together


Gestalt grouping principle; we group similar figures together


Gestalt grouping principle; our tendency to perceive smooth, continuous patterns rather than discontinuous ones


Gestalt grouping principle; when objects uniform (in color or texture) are linked (no space exists between them) we perceive them as a single unit


Gestalt grouping principle; we fill in "gaps" to create a full, complete object

illusory contours

imagined "boundaries" between one object and other; often created by the perception of "lines" that divide areas of color or texture

depth perception

the ability to see objects in three dimensions although the images that strike the retina are two-dimensional; allows us to judge distance

visual cliff

laboratory device for testing depth perception among infants and young animals; its use demonstrated that, among most species, animals have the ability to perceive depth by the time they are mobile

binocular cues

depth cues that require the combined input of both eyes

monocular cues

depth cues that only require input from one eye; often used in 2D art to create illusion of depth

retinal disparity

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


a binocular cue for perceiving depth; the more the eyes strain to turn inwards to view an object, the closer the object is (note: only a factor at close ranges)

Wolfgang Kohler

credited with founding Gestalt Psychology

relative height

monocular cue for depth perception; we perceive objects higher in our visual field to be farther away. Explanation for why the "bottom" of a figure-ground illusion usually is interpreted as the "figure"

relative size

monocular cue for depth perception; if we assume two objects are similar in size, most people perceive the one that casts the smaller retinal image to be farther away


monocular cue for depth perception; if one object partially blocks our view of another object, we perceive it as closer

linear perspective

monocular cue for depth perception; parallel lines, such as railroad tracks, appear to converge with distance. The more they converge, the greater the perceived distance

light and shadow

monocular cue for depth perception; nearby objects reflect more light to our eyes...thus, given two identical objects, the dimmer one seems farther away. Also, shading produces a sense of depth consistent with our assumption that light comes from above.

relative motion

monocular cue for depth perception; as we move, stationary objects seem to "move" as well. Objects above a fixation point move "with" us, objects below the fixation point move "past" us.

relative clarity

monocular cue for depth perception; objects that seem "fuzzier" or less clear are perceived to be farther away.

texture gradient

monocular cue for depth perception; a gradual change from course, distinct texture to fine, indistinct texture signals increasing distance

phi phenomenon

an illusion of movement created when two or more adjacent lights blink on and off in rapid succession

stroboscopic movement

the brain's perception of continuous movement in a rapid series of slightly varying images; this is how we perceive motion in film and animation

perceptual constancy

perceiving objects as unchanging (having consistent shapes, size, lightness, and color) even as illumination and retinal images change

perceptual adaptation

the ability to adjust to an altered perceptual reality; in vision, the ability to adjust to an artificially displaced or inverted visual field (as when wearing visual displacement goggles).

perceptual set

mental predisposition to perceive one thing and not another (for example, due to suggestion or expectations based on prior learning)

human factors psychology

Branch of psychology that explores how people & machines interact and how physical environment can be adapted to human behaviors

extrasensory perception (ESP)

the controversial claim that perception can occur apart from sensory input; includes telepathy, clairvoyance, and precognition


the study of paranormal phenomena, including ESP and psychokinesis


mind-to-mind communication; a person sending thoughts to another or perceiving another's thoughts


perceiving remote events, such as sensing that a friend's house is on fire


perceiving future events, such as a political leader's death or a sporting event's outcome


ability to move objects with one's mind

Ganzfeld procedure

laboratory procedure used to test powers of extrasensory perception by reducing the distractions of other sensory information (e.g. noise cancelling headphones, ping-pong balls over the eyes, etc.)

visual capture

the phenomenon that occurs when vision overtakes some other, conflicting sensory input

change blindness

when paying attention to a specific aspect of a visual scene, we may fail to notice other fairly obvious changes or presentations of stimuli; demonstrated by the door study and the gorilla illusion

McGurk effect

the same sound (e.g. "ba") can be perceived differently (e.g. "pa" or "fa") when the visual image of the mouth pronouncing it is changed

Troxler effect

perception of motion in absence of any other visual perception

bipolar cells

second layer of neurons in the retina that transmit impulses from rods and cones to ganglion cells; rods share these, but cones do not

retinal ganglion cells

the third layer of retinal neurons whose axons leave the eyeball and form the optic nerve.

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