1.6a-1.6b

parallel processing

processing

multiple aspects of a stimulus or

problem simultaneously.

opponent processing theory

theory that opposing retinal

processes (red-green, blue-

yellow, 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.

feature detectors

nerve cells

in the brain's visual cortex that

respond to specific features of

the stimulus, such as shape,

angle, or movement.

Young-Helmholtz

trichromatic (three-color)

theory

the theory that the retina

contains three different types

of 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.

fovea

the central focal point

in the retina, around which the

eye's cones cluster.

blind spot

the point at which

the optic nerve leaves the eye,

creating a "blind" spot because

no receptor cells are located

there,

optic nerve

the nerve that

carries neural impulses from the

eye to the brain.

cones

retinal receptors that

are concentrated near the

center of the retina and that

function in daylight or in well-lit

conditions. Cones detect fine

detail and give rise to color

sensations.

rods

retinal receptors that

detect black, white, and gray, and

are sensitive to movement. Rods

are necessary for peripheral and

twilight vision, when cones don't

respond.

accommodation

the process

by which the eye's lens changes

shape to focus images of near or

far objects on the retina.

retina

the light-sensitive back

inner surface of the eye, containing

the receptor rods and cones plus

layers of neurons that begin the

processing of visual information.

lens

the transparent structure

behind the pupil that changes

shape to help focus images on

the retina.

iris

ring of muscle tissue that

forms the colored portion of

the eye around the pupil and

controls the size of the pupil

opening.

pupil

the adjustable opening

in the center of the eye through

which light enters.

cornea

the eye's clear,

protective outer layer, covering

the pupil and iris.

intensity

the amount of

energy in a light wave or sound

wave, which influences what

we perceive as brightness or

loudness. Intensity is determined

by the wave's amplitude

hue

the dimension of color that

is determined by the wavelength

of light; what we know as the

color names blue, green, and so

forth.

wavelength

the distance from

the peak of one light wave

or sound wave to the peak

of the next. Electromagnetic

wavelengths vary from the short

gamma waves to the long pulses

of radio transmission.

sensory adaptation

diminished

sensitivity as a consequence of

constant stimulation.

webers law

the principle that,

to be perceived as different, two

stimuli must differ by a constant

minimum percentage

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

subliminal

below one's

absolute threshold for conscious

awareness.

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

alertness.

absolute threshold

the

minimum stimulus energy

needed to detect a particular

stimulus 50 percent of the time.

psycho physics

the study

of relationships between the

physical characteristics of stimuli,

such as their intensity, and our

psychological experience of them.

transduction

conversion of one

form of energy into another. In

sensation, the transforming of

physical energy, such as sights,

sounds, and smells, into neural

impulses the brain can interpret.

top-down processing

information processing

guided by higher-level mental

processes, as when we construct

perceptions drawing on our

experience and expectations.

bottom up processing

information processing that

begins with the sensory

receptors and works up to the

brain's integration of sensory.

information.

perception

the process by

which our brain organizes and

interprets sensory information,

enabling us to recognize objects

and events as meaningful.

sensory receptors

sensory

nerve endings that respond to

stimuli.

sensation

the process by

which our sensory receptors

and nervous system receive and

represent stimulus energies from

our environment.

Priming

the activation, often

unconsciously, of certain

associations, thus predisposing

one's perception, memory, or

response.