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 gamma rays to the long pulses of radio transmission

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

intensity

the amount of energy in a light wave or sound waves, which influences what we perceive as brightness or loudness. Intensity is determined by the wave's amplitude (height)

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

accomodation

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, and are sensitive to movement; necessary for peripheral and twilight vision, when cones don't respond

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

optic nerve

the nerve that carries nerve 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

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

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

feature detectors

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

parallel processing

processing many aspects of a problem simultaneously; the brain's natural mode of information processing for many functions

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 cue

a depth cue, such as retinal disparity, that depends on the use of two eyes

retinal disparity

a binocular cue for perceiving depth. By comparing retinal images from the two eyes, the brain computes distance- the greater the disparity (difference) between the two images, the closer the object

monocular cue

a depth cue, such as interposition or 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 color, brightness, shape, and size) even as illumination and retinal images change

perceptual adaptation

the ability to adjust to changed sensory input, including an artificially displaced or even inverted visual field