Sensory and Perception

sensation

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

perception

A process of organizing and interpreting sensory information, enabling us to recognize meaningful objects and events.

bottom-up processing

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

top-down processing

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

selective attention

The focusing of conscious awareness on a particular stimulus

inattentional blindness

Failing to see visible objects when our attention is directed elsewhere

change blindness

Failing to notice changes in the environment

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.

psychophysics

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

absolute threshold

Minimum stimulation needed to detect a particular stimulus 50% of the time

signal detection theory

A theory predicting how and when we detect the presence of a faint stimulus (signal) amid background stimulation (noise). Assumes there is no single absolute threshold and that detection depends partly on a person's experience, expectations, motivation, and level of fatigue.

subliminal

Below one's absolute threshold for conscious awareness

priming

the activation, often unconsciously, of certain associations, thus predisposing one's perception, memory, or response.

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.)

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

perceptual set

A mental predisposition to perceive one thing and not another

extrasensory perception (ESP)

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

parapsychology

the study of paranormal phenomena, including ESP and psychokinesis

wavelength

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 transmissions.

hue

the dimension of color that is determined by the wavelength of light; what we know as the color names: blue, green, etc.

intensity

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

pupil

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

iris

A ring of muscle tissue that forms the colored portion of the eye around the pupil and controls the size of the pupil opening.

lens

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

retina

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

accommodation

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

rods

retinal receptors that detect black, white, and gray; necessary for peripheral and twilight vision, when cones do not respond.

cones

retinal receptors that acre connected near the center of the retina and that function in daylight or well-lit conditions. They detect fine detail and give rise to color sensations.

cornea

protects the eye and bends light to provide focus

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, creating a "blind" spot because no receptor cells are located there.

fovea

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 stimulus, such as shape, angle, or movement

parallel processing

The processing of many aspects of a problem simultaneously; the brain's natural mode of information processing for many functions, including vision. Contrasts 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 color 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. For example, some cells are stimulated by green and inhibited by red; others are stimulated by red and inhibited by green

gestalt

An organized whole. Gestalt psychologists emphasized our tendency to integrate pieces of information into meaningful wholes.

figure-ground

The organization of the visual field into objects (the figures) that stand out from their surroundings (the ground).

grouping

the perceptual tendency to organize stimuli into coherent groups

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

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

binocular cues

Depth cues, such as retinal disparity and convergence, that depend on the use of two eyes

retinal disparity

a binocular cue for perceiving depth; by comparing images from the two eyeballs, the brain computes distance - the greater the disparity (difference) between the two images, the close the object

monocular cues

Depth cues, such as interposition and linear perspective, available to either eye alone

phi phenomenon

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

perceptual constancy

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

color constancy

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

perceptual adaptation

In vision, the ability to adjust to an artificially displaced or even inverted visual field

audition

The sense or act of hearing

frequency

the number of complete wavelengths that pass a point in a given time (for example, per second)

pitch

A tone's experienced highness or lowness; depends on frequency.

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.

cochlea

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

inner ear

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

sensorineural hearing loss

Hearing loss caused by damage to the cochlea's receptor cells or to the auditory nerves; also called nerve deafness

conduction hearing loss

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

cochlear implant

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

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

gate-control theory

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

kinesthesia

the system for sensing the position and movement of individual body parts

vestibular sense

The sense of body movement and position, including the sense of balance

sensory interaction

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

embodied cognition

In psychological science, the influence of bodily sensations, gestures, and other states on cognitive preferences and judgments

hair cells

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

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).

David Hubel & Torsten Wiesel

discovered "feature detectors" within the brain

synaesthesia

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

cocktail party effect

ability to selectively attend to one voice among many

proximity

Gestalt grouping principle; we group nearby figures together

similarity

Gestalt grouping principle; we group similar figures together

continuity

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

connectedness

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

closure

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

convergence

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; also conducted studies of insight learning in chimps

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

interposition

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

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; a classic example of "visual capture"

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.

gustation

sense of taste

nociceptors

Nerve endings that signal the sensation of pain.