Midterm II

Question 1

S-cone

Answer 1

A cone that is preferentially sensitive to short wavelengths; colloquially (but not entirely accurately) known as a “blue cone.”

Question 2

M-cone

Answer 2

A cone that is preferentially sensitive to middle wavelengths; colloquially (but not entirely accurately) known as a “green cone.”

Question 3

L-cone

Answer 3

A cone that is preferentially sensitive to long wavelengths; colloquially (but not entirely accurately) known as a “red cone.”

Question 4

spectral sensitivity

Answer 4

Refering to the sensitivity of a cell or a device to different wavelengths on the electromagnetic spectrum.

Question 5

photopic

Answer 5

Referring to light intensities that are bright enough to stimulate the cone receptors and bright enough to “saturate” the rod receptors (that is, drive them to their maximum responses).

Question 6

scotopic

Answer 6

Referring to light intensities that are bright enough to stimulate the rod receptors but too dim to stimulate the cone receptors.

Question 7

principle of univariance

Answer 7

The fact that an infinite set of different wavelength-intensity combinations can elicit exactly the same response from a single type of photoreceptor. One photoreceptor type cannot make color discriminations based on wavelength.

Question 8

trichromatic theory of color vision or trichromacy

Answer 8

The theory that the color of any light is defined in our visual system by the relationships of three numbers—the outputs of three receptor types now known to be the three cones. Also called the Young-Helmholtz theory.

Question 9

metamers

Answer 9

Different mixtures of wavelengths that look identical. More generally, any pair of stimuli that are perceived as identical in spite of physical differences.

Question 10

additive color mixture

Answer 10

A mixture of lights. If light A and light B are both reflected from a surface to the eye, in the perception of color the effects of those two lights add together.

Question 11

subtractive color mixture

Answer 11

A mixture of pigments. If pigments A and B mix, some of the light shining on the surface will be subtracted by A, and some by B. Only the remainder contributes to the perception of color.

Question 12

lateral geniculate nucleus (LGN)

Answer 12

A structure in the thalamus, part of the midbrain, that receives input from the retinal ganglion cells and has input and output connections to the visual cortex.

Question 13

cone-opponent cell

Answer 13

A cell type—found in the retina, lateral geniculate nucleus, and visual cortex—that, in effect, subtracts one type of cone input from another.

Question 14

circadian

Answer 14

Referring to cells in the magnocellular layers of the lateral geniculate nucleus of the thalamus. Magno from the Greek for “large” referring to the size of the cells.

Question 15

melanopsin

Answer 15

A photopigment, found in a class of photoreceptive retinal ganglion cells, that is sensitive to ambient light.

Question 16

color space

Answer 16

The three-dimensional space, established because color perception is based on the outputs of three cone types, that describes the set of all colors.

Question 17

opponent color theory

Answer 17

The theory that perception of color is based on the output of three mechanisms, each of them resulting from an opponency between two colors: red-green, blue-yellow, and black-white.

Question 18

unique hue

Answer 18

Any of four colors that can be described with only a single color term: red, yellow, green, blue. Other colors (e.g., purple or orange) can be described as compounds (reddish blue, reddish yellow).

Question 19

double-opponent cell

Answer 19

A cell type, found in the visual cortex, in which one region is excited by one cone type, combination of cones, or color and inhibited by the opponent cones or color (e.g., R+/G–). Another adjacent region would be inhibited by the first input and excited by the second (thus, in this example, R–/G+).

Question 20

single-opponent cell

Answer 20

Another way to refer to cone-opponent cells, in order to differentiate them from double-opponent cells.

Question 21

achromatopsia

Answer 21

An inability to perceive colors that is caused by damage to the central nervous system.

Question 22

qualia

Answer 22

In philosophy, private conscious experiences of sensation or perception.

Question 23

basic color terms

Answer 23

Color words that are monolexemic (single words “blue” not, “sky blue”), used with high frequency, and have meanings that are agreed upon by speakers of a language.

Question 24

cultural relativism

Answer 24

In sensation and perception, the idea that basic perceptual experiences (e.g., color perception) may be determined in part by the cultural environment.

Question 25

deuteranope

Answer 25

An individual who suffers from color blindness that is due to the absence of M-cones.

Question 26

protanope

Answer 26

An individual who suffers from color blindness that is due to the absence of L-cones.

Question 27

tritanope

Answer 27

An individual who suffers from color blindness that is due to the absence of S-cones.

Question 28

color-anomalous

Answer 28

A better term for what is usually called “color-blind.” Most “color-blind” individuals can still make discriminations based on wavelength. Those discriminations are different from the norm—that is, anomalous.

Question 29

cone monochromat

Answer 29

An individual with only one cone type. Cone monochromats are truly color-blind.

Question 30

rod monochromat

Answer 30

An individual with no cones of any type. In addition to being truly color-blind, rod monochromats are badly visually impaired in bright light.

Question 31

agnosia

Answer 31

A failure to recognize objects in spite of the ability to see them. Agnosia is typically due to brain damage.

Question 32

anomia

Answer 32

An inability to name objects in spite of the ability to see and recognize them (as shown by usage). Anomia is typically due to brain damage.

Question 33

color contrast

Answer 33

A color perception effect in which the color of one region induces the opponent color in a neighboring region.

Question 34

color assimilation

Answer 34

A color perception effect in which two colors bleed into each other, each taking on some of the chromatic quality of the other.

Question 35

unrelated color

Answer 35

A color that can be experienced in isolation.

Question 36

related color

Answer 36

A color, such as brown or gray, that is seen only in relation to other colors. For example, a “gray” patch in complete darkness appears white.

Question 37

negative afterimage

Answer 37

An afterimage whose polarity is the opposite of the original stimulus. Light stimuli produce dark negative afterimages. Colors are complementary; for example, red produces green, and yellow produces blue.

Question 38

adapting stimulus

Answer 38

A stimulus whose removal produces a change in visual perception or sensitivity.

Question 39

neutral point

Answer 39

The point at which an opponent color mechanism is generating no signal. If red-green and blue-yellow mechanisms are at their neutral points, a stimulus will appear achromatic. (The black-white process has no neutral point.)

Question 40

color constancy

Answer 40

The tendency of a surface to appear the same color under a fairly wide range of illuminants.

Question 41

illuminant

Answer 41

The light that illuminates a surface.

Question 42

spectral reflectance function

Answer 42

The percentage of a particular wavelength that is reflected from a surface.

Question 43

spectral power distribution

Answer 43

The physical energy in a light as a function of wavelength.

Question 44

reflectance

Answer 44

The percentage of light hitting a surface that is reflected and not absorbed into the surface. Typically reflectance is given as a function of wavelength.

Question 45

absolute metrical depth cue

Answer 45

A depth cue that provides quantifiable information about distance in the third dimension (e.g., his nose sticks out 4 centimeters in front of his face).

Question 46

accommodation

Answer 46

The process by which the eye changes its focus (in which the lens gets fatter as gaze is directed toward nearer objects).

Question 47

aerial perspective or haze

Answer 47

A depth cue based on the implicit understanding that light is scattered by the atmosphere. More light is scattered when we look through more atmosphere. Thus, more distant objects are subject to more scatter and appear fainter, bluer, and less distinct.

Question 48

anamorphosis or anamorphic projection

Answer 48

Use of the rules of linear perspective to create a two-dimensional image so distorted that it looks correct only when viewed from a special angle or with a mirror that counters the distortion.

Question 49

Bayesian approach

Answer 49

A way of formalizing the idea that our perception is a combination of the current stimulus and our knowledge about the conditions of the world—what is and is not likely to occur. The Bayesian approach is stated mathematically as Bayes’ theorem—P(A|O) = P(A) x P(O|A)/P(O)—which enables us to calculate the probability (P) that the world is in a particular state (A) given a particular observation (O).

Question 50

binocular

Answer 50

With two eyes.

Question 51

binocular depth cue

Answer 51

A depth cue that relies on information from both eyes. Stereopsis is the primary example in humans, but convergence and the ability of two eyes to see more of an object than one eye sees are also binocular depth cues.

Question 52

binocular disparity

Answer 52

The differences between the two retinal images of the same scene. Disparity is the basis for stereopsis, a vivid perception of the three-dimensionality of the world that is not available with monocular vision.

Question 53

binocular rivalry

Answer 53

The competition between the two eyes for control of visual perception, which is evident when completely different stimuli are presented to the two eyes.

Question 54

binocular summation

Answer 54

The combination (or “summation”) of signals from each eye in ways that make performance on many tasks better with both eyes than with either eye alone.

Question 55

continuity constraint

Answer 55

In stereopsis, the observation that, except at the edges of objects, neighboring points in the world lie at similar distances from the viewer. This is one of several constraints that have been proposed as helpful in solving the correspondence problem.

Question 56

convergence

Answer 56

The ability of the two eyes to turn inward, often used in order to place the two images of a feature in the world on corresponding locations in the two retinal images (typically on the fovea of each eye). Convergence reduces the disparity of that feature to zero (or nearly zero).

Question 57

correspondence problem

Answer 57

1. In binocular vision, the problem of figuring out which bit of the image in the left eye should be matched with which bit in the right eye. The problem is particularly vexing when the images consist of thousands of similar features, like dots in random dot stereograms. 2.In motion detection, the problem faced by the motion detection system of knowing which feature in frame 2 corresponds to a particular feature in frame 1.

Question 58

corresponding retinal points

Answer 58

Two monocular images of an object in the world are said to fall on corresponding points if those points are the same distance from the fovea in both eyes. The two foveas are also corresponding points.

Question 59

critical period

Answer 59

A phase in the life span during which abnormal early experience can alter normal neuronal development. Critical periods are proposed for the development of binocular vision and development of a first human language.

Question 60

crossed disparity

Answer 60

The sign of disparity created by objects in front of the plane of fixation (the horopter). The term crossed is used because images of objects located in front of the horopter appear to be displaced to the left in the right eye, and to the right in the left eye.

Question 61

Cyclopean

Answer 61

Referring to stimuli that are defined by binocular disparity alone. Named after the one-eyed Cyclops of Homer’s Odyssey.

Question 62

dichoptic

Answer 62

Referring to the presentation of two different stimuli, one to each eye. Different from binocular presentation, which could involve both eyes looking at a single stimulus.

Question 63

diplopia

Answer 63

Double vision. If visible in both eyes, stimuli falling outside of Panum’s fusional area will appear diplopic.

Question 64

divergence

Answer 64

The ability of the two eyes to turn outward, often used in order to place the two images of a feature in the world on corresponding locations in the two retinal images (typically on the fovea of each eye). Divergence reduces the disparity of that feature to zero (or nearly zero).

Question 65

esotropia

Answer 65

Strabismus in which one eye deviates inward.

Question 66

Euclidean

Answer 66

Referring to the geometry of the world, so named in honor of Euclid, the ancient Greek geometer of the third century BCE. In Euclidean geometry, parallel lines remain parallel as they are extended in space, objects maintain the same size and shape as they move around in space, the internal angles of a triangle always add to 180 degrees, and so forth.

Question 67

exotropia

Answer 67

Strabismus in which one eye deviates outward.

Question 68

familiar size

Answer 68

A depth cue based on knowledge of the typical size of objects like humans or pennies.

Question 69

free fusion

Answer 69

The technique of converging (crossing) or diverging the eyes in order to view a stereogram without a stereoscope.

Question 70

horopter

Answer 70

The location of objects whose images lie on corresponding points. The surface of zero disparity.

Question 71

linear perspective

Answer 71

A depth cue based on the fact that lines that are parallel in the three-dimensional world will appear to converge in a two-dimensional image.

Question 72

metrical depth cue

Answer 72

A depth cue that provides quantitative information about distance in the third dimension.

Question 73

monocular

Answer 73

With one eye.

Question 74

monocular depth cue

Answer 74

A depth cue that is available even when the world is viewed with one eye alone.

Question 75

motion parallax

Answer 75

An important depth cue that is based on head movement. The geometric information obtained from an eye in two different positions at two different times is similar to the information from two eyes in different positions in the head at the same time.

Question 76

nonmetrical depth cue

Answer 76

A depth cue that provides information about the depth order (relative depth) but not depth magnitude (e.g., his nose is in front of his face).

Question 77

occlusion

Answer 77

A cue to relative depth order in which, for example, one object obstructs the view of part of another object.

Question 78

optic flow

Answer 78

The pattern of apparent motion of objects in a visual scene produced by the relative motion between the observer and the scene.

Question 79

Panum’s fusional area

Answer 79

The region of space, in front of and behind the horopter, within which binocular single vision is possible.

Question 80

pictorial depth cue

Answer 80

A cue to distance or depth used by artists to depict three-dimensional depth in two-dimensional pictures.

Question 81

positivism

Answer 81

A philosophical position arguing that all we really have to go on is the evidence of the senses, so the world might be nothing more than an elaborate hallucination.

Question 82

probability summation

Answer 82

The increased detection probability based on the statistical advantage of having two (or more) detectors rather than one.

Question 83

projective geometry

Answer 83

For purposes of studying perception of the three-dimensional world, the geometry that describes the transformations that occur when the three-dimensional world is projected onto a two-dimensional surface. For example, parallel lines do not converge in the real world, but they do in the two-dimensional projection of that world.

Question 84

random dot stereogram (RDS)

Answer 84

A stereogram made of a large number (often in the thousands) of randomly placed dots. Random dot stereograms contain no monocular cues to depth. Stimuli visible stereoscopically in random dot stereograms are Cyclopean stimuli.

Question 85

realism

Answer 85

A philosophical position arguing that there is a real world to sense.

Question 86

relative height

Answer 86

As a depth cue, the observation that objects at different distances from the viewer on the ground plane will form images at different heights in the retinal image. Objects farther away will be seen as higher in the image.

Question 87

relative metrical depth cue

Answer 87

A depth cue that could specify, for example, that object A is twice as far away as object B without providing information about the absolute distance to either A or B.

Question 88

relative size

Answer 88

A comparison of size between items without knowing the absolute size of either one.

Question 89

stereoacuity

Answer 89

A measure of the smallest binocular disparity that can generate a sensation of depth.

Question 90

stereoblindness

Answer 90

An inability to make use of binocular disparity as a depth cue. This term is typically used to describe individuals with vision in both eyes. Someone who has lost one (or both) eyes is not typically described as “stereoblind.”

Question 91

stereopsis

Answer 91

The ability to use binocular disparity as a cue to depth.

Question 92

stereoscope

Answer 92

A device for simultaneously presenting one image to one eye and another image to the other eye. Stereoscopes can be used to present dichoptic stimuli for stereopsis and binocular rivalry.

Question 93

strabismus

Answer 93

A misalignment of the two eyes such that a single object in space is imaged on the fovea of one eye and on a nonfoveal area of the other (turned) eye.

Question 94

suppression

Answer 94

In vision, the inhibition of an unwanted image. Suppression occurs frequently in people with strabismus.

Question 95

texture gradient

Answer 95

A depth cue based on the geometric fact that items of the same size form smaller images when they are farther away. An array of items that change in size smoothly across the image will appear to form a surface tilted in depth.

Question 96

tilt aftereffect

Answer 96

The perceptual illusion of tilt, produced by adaptation to a pattern of a given orientation.

Question 97

uncrossed disparity

Answer 97

The sign of disparity created by objects behind the plane of fixation (the horopter). The term uncrossed is used because images of objects located behind the horopter will appear to be displaced to the right in the right eye, and to the left in the left eye.

Question 98

uniqueness constraint

Answer 98

In stereopsis, the observation that a feature in the world is represented exactly once in each retinal image. This constraint simplifies the correspondence problem.

Question 99

vanishing point

Answer 99

The apparent point at which parallel lines receding in depth converge.

Question 100

Vieth-Müller circle

Answer 100

The location of objects whose images fall on geometrically corresponding points in the two retinas. If life were simple, this circle would be the horopter, but life is not simple.