Light containing wavelengths from across the visible spectrum, with no really dominant wavelengths; perceived as more or less colorless (i.e., a shade of gray).
achromatic light (or white light)
Loss of color vision caused by brain damage.
A mixture of different-colored lights; called "additive" because the perceived color of the mixture is the result of adding together all the wavelengths in all the lights in the mixture.
additive color mixture
A kind of photopigment bleaching that results from exposure to relatively intense light consisting of a narrow range of wavelengths.
A 2-D depiction in which hue varies around the circumference and saturation varies along any radius.
The tendency to see a surface as having the same color under illumination by lights with very different spectral power distributions.
A 3-D depiction in which hue varies around the circumference, saturation varies along any radius, and brightness varies vertically.
The ability to see differences between lights of different wavelengths.
Pairs of colors that, when combined in equal proportion, are perceived as a shade of gray.
A condition in which a person has rods and only one type of cone.
A condition in which a person has L-cones and S-cones but lacks M-cones.
A condition in which a person has only two types of cones, instead of the normal three; in all such cases, the person has a limited form of color vision but cannot discriminate as many colors as a person with all three cone types.
Light that consists of more than one wavelength.
The quality usually referred to as "color"--that is, blue, green, yellow, red, and so on; the perceptual characteristic most closely associated with the wavelength of light.
An experimental technique in which the person cancels out any perception of a particular color (e.g., yellow) in a test light by adding light of the complementary color (e.g., blue).
A test using configurations of multicolored disks with embedded symbols; the symbols can be seen by people with normal color vision but not by people with particular color vision deficiencies.
Ishihara color vision test
The tendency to see a surface as having the same lightness under illumination by very different amounts of light.
Any two stimuli that are physically different but are perceived as identical.
A condition in which a person has only rods or has only rods and one type of cone; in either case, the person is totally color-blind, perceiving everything in shades of gray.
Light that consists of only one wavelength.
A photopigment molecule's loss of ability to absorb light for a period after undergoing photoisomerization.
Picture elements in the display screen of a color monitor; a pixel consists of three subelements, each designed to emit the light of one of three primary colors--red, green, or blue.
Any three colors that can be combined in different proportions to produce a range of other colors.
With regard to cones, the principle that absorption of a photon of light results in the same response regardless of the wavelength of the light.
principle of univariance
A condition in which a person has M-cones and S-cones but lacks L-cones.
A condition in which a person has rods only, with no cones.
The vividness (or purity or richness) of a hue.
The intensity (power) of a light at each wavelength in the visible spectrum.
spectral power distribution (SPD)
The proportion of light that a surface reflects at each wavelength.
The probability that a cone's photopigment will absorb a photon of light of any given wavelength.
spectral sensitivity function
A mixture of different-colored substances; called "subtractive" because the light reflected from the mixture has certain wavelengths subtracted (absorbed) by each substance in the mixture.
subtractive color mixture
A condition in which a person has L-cones and M-cones but lacks S-cones.
The portion of the electromagnetic spectrum in the range of about 400 to about 700 nm; within this range, people with normal vision perceive differences in wavelength as differences in color.
A dynamic depth cue--the gradual revealing ("de-occlusion") of an object as it emerges from behind another one.
A room specially designed to create an illusory perception of depth; when viewed with one eye through a peephole, all of the room's trapezoidal surfaces look rectangular.
A stereogram in which the two photographs taken from adjacent camera positions are printed in contrasting colors and then superimposed; an observer who views an anaglyph with special glasses in which one lens filters out one of the colors and the other lens filters out the other color will see a single image in depth.
A lighting-based depth cue--the farther away an object is, the more air the light must pass through to reach us and the more that light can be scattered, with the result that distant objects appear less distinct than nearby objects.
Neurons that respond best to the stimulation of their receptive fields in both eyes simultaneously.
A depth cue based on differences in the relative positions of the retinal images of objects in the two eyes.
The problem of determining which features in the retinal image in one eye correspond to which features in the retinal image in the other eye.
A point on the left retina and a point on the right retina that would coincide if the two retinas were superimposed--for example, the foveas of the two eyes.
A type of binocular disparity produced by an object that is closer than the horopter--you would have to "cross" your eyes to look at it.
A dynamic depth cue--the gradual hiding (occlusion) of an object as it passes behind another one.
Size-distance invariance of retinal afterimages--the perceived size of an afterimage is proportional to the distance of the surface on which it's "projected."
A size-based depth cue--knowing the retinal image size of a familiar object at a familiar distance lets us use its retinal image size to gauge its distance.
An imaginary surface defined by the locations in a scene from which objects would project retinal images at corresponding points.
A size-based depth cue--parallel lines appear to converge as they recede in depth.
Cues that are based on the retinal image and that provide information about depth even with only one eye open.
monocular depth cues
A dynamic depth cue--the difference in the speed and direction with which objects appear to move in the retinal image as an observer moves within a scene.
A point on the left retina and a point on the right retina that wouldn't coincide if the two retinas were superimposed--for example, the fovea of one eye and a point 4 mm to the right of the fovea in the other eye.
Cues that are based on feedback from the oculomotor muscles controlling the shape of the lens and the position of the eyes.
oculomotor depth cues
A dynamic depth cue--the relative motions of objects and surfaces in the retinal image as the observer moves forward or backward through a scene.
A position-based depth cue--in scenes where one object partially hides (occludes) another object, the occlusion indicates that the former is closer than the latter.
partial occlusion (or interposition)
A stereogram in which both images consist of a grid of randomly arranged black and white dots, identical except for the displacement of a portion in one image relative to the other; an observer who views a random dot stereogram in a stereoscope or as an anaglyph will see a single image with the displaced portion in depth.
random dot stereogram (RDS)
A position-based depth cue--the relative height of the objects in the retinal image with respect to the horizon--or with respect to eye level if there is no visible horizon--provides information about the objects' relative distance from the observer.
A size-based depth cue--under the assumption that two or more objects are about the same size, the relative size of their retinal images can be used to judge their relative distances.
A type of perceptual constancy--the tendency to perceive an object's shape as constant despite changes in the shape of the object's retinal image due to the object's changing orientation.
The relation between perceived shape and perceived slant: the perceived shape of an object depends on its perceived slant, and vice versa.
A type of perceptual constancy--the tendency to perceive an object's size as constant despite changes in the size of the object's retinal image due to the object's changing distance from the observer.
A depth cue in scenes in which the size-distance relation is apparent.
The relation between perceived size and perceived distance: the perceived size of an object depends on its perceived distance, and vice versa.
The farther away an object is from the observer, the smaller is its retinal image.
Cues that provide information about depth on the basis of the position of objects in the retinal image, the size of the retinal image, and the effects of lighting in the retinal image.
static monocular depth cues
Two depictions of a scene that differ in the same way as an observer's two retinal images of that scene would differ; an observer who simultaneously views one image with one eye and the other image with the other eye (as in a stereoscope) will see a combined image in depth.
The vivid sense of depth arising from the visual system's processing of the different retinal images in the two eyes.
stereopsis (or stereoscopic depth perception)
A size-based depth cue--if surface variations or repeated elements of a surface are fairly regular in size and spacing, the retinal image size of these equal-size features decreases as their distance increases.
A type of binocular disparity produced by an object that is farther away than the horopter--you would have to "uncross" your eyes to look at it.
The angle subtended by an object in the field of view.
A type of binocular disparity in which the retinal image of an object falls at corresponding points in the two eyes.
A region of the posterior parietal lobe thought to be involved in grasping movements.
anterior intraparietal area (AIP)
The impossibility of determining the actual direction of motion of a stimulus by the response of a single neuron that "sees" the stimulus only through a small "aperture" (the neuron's receptive field) and "sees" only the component of motion in the neuron's preferred direction.
A visual illusion in which two stimuli separated in time and location are perceived as a single stimulus moving between the two locations.
A display in which four symmetrically placed stimuli presented at alternating moments in time are perceived as two stimuli in apparent motion.
apparent motion quartet
A copy of an eye-movement command from the superior colliculus to the extraocular muscles, sent to the brain to inform the visual system about upcoming eye movements; used to ensure a stable visual experience even during eye movements.
corollary discharge signal (CDS)
A region of the posterior parietal lobe in monkeys that is involved in the control of eye movements, including intended eye movements; an analogous region exists in the human brain.
lateral intraparietal area (LIP)
A strategy for catching a fly ball by which the fielder runs in a path and at a speed such that the ball appears to travel upward in a straight line at a constant speed.
linear optical trajectory (LOT)
A region of the posterior parietal lobe involved in planning reach movements.
medial intraparietal area (MIP)
A visual illusion in which a stationary element of the visual scene appears to be moving in a direction opposite to the direction of motion experienced during the immediately preceding time interval.
motion aftereffect (MAE)
A display in which biological motion is made visible by attaching small lights at critical locations on an organism's body (e.g., at a person's arm, leg, and hip joints) and then shooting a video of the organism in motion in darkness.
A display in which a grid is filled with tiny, randomly placed black and white square dots and in which the dots in a region of the grid are then moved rigidly together as a group; the shape of the region is visible when the dots move but not when they're still.
random dot kinematogram
Brief, rapid eye movements that change the focus of gaze from one location to another.
saccadic eye movements (or saccades)
The visual system's suppression of neural signals from the retina during saccadic eye movements.
Eye movements made to track a moving object or to track a stationary object while the head is moving.
smooth pursuit eye movements
Eye movements that occur when the gaze shifts between focusing on objects at different distances.
vergence eye movements
plots of percentage of light reflected for specific wavelengths
objects that preferentially reflect some wavelengths (called selective reflectance)
Chromatic colors or hues
contain no hues (white, black, gray tones)
from dark to light
which changes perceived brightness
adding white to a color results in less saturated color.
Saturation (vividness of a hue)
Transparent objects, such as liquids, selectively allow wavelengths to pass through
background of object can affect color perceptions
Simultaneous color contrast
a mixture of different-colored lights called additive because the perceived color of the mixture is the result of adding together all the wavelengths in all the lights in the mixture.
Additive color mixture
with regard to cones, the principal that absorption of a photon of light results in the same response regardless of the wavelength of the light.
Principle of Univariance
a person who needs only one wavelength to match any color
person who needs only two wavelengths to match any color
needs three wavelengths in different proportions than a normal trichromat.
trichromatic vision on one eye and dichromatic in the other
Explains responses of the cones in the Retina
explains neural response for cells connected to the cones further in the brain
this approach focuses on information in the retinal image that is correlated with depth in the scene, the association becomes automatic through repeat exposure
Cue Approach to Depth Perception
inward movement of the eyes when we focus on nearby objects
change in the shape of the lens when we focus on objects at different distance
pictorial cues sources of depth information that come from 2-D images, such as pictures
Monocular cues come from one eye
when on object partially covers another
close objects in direction of movement glide rapidly past but objects in the distance appear to move slowly
Motion parallax/optic flow
distance objects are fuzzy and have a blue tint
Indicate where objects are located perspective
depth information provided by binocular disparity
an object is physically moving
basis of motion in movies and TV
stationary stimuli are presented in slightly different location basis of movement in movies and TV
movement of one object results in the perception of movement in another object
a visual illusion in which a stationary element of the visual scene appears to be moving in a direction of motion experienced during the immediately preceding time interval. (Waterfall illusion).