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Flashcards in Midterm II Deck (100):
1

S-cone

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

2

M-cone

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

3

L-cone

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

4

spectral sensitivity

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

5

photopic

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).

6

scotopic

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

7

principle of univariance

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.

8

trichromatic theory of color vision or trichromacy

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.

9

metamers

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

10

additive color mixture

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.

11

subtractive color mixture

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.

12

lateral geniculate nucleus (LGN)

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.

13

cone-opponent cell

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

14

circadian

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.

15

melanopsin

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

16

color space

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

17

opponent color theory

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.

18

unique hue

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).

19

double-opponent cell

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+).

20

single-opponent cell

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

21

achromatopsia

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

22

qualia

In philosophy, private conscious experiences of sensation or perception.

23

basic color terms

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.

24

cultural relativism

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

25

deuteranope

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

26

protanope

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

27

tritanope

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

28

color-anomalous

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.

29

cone monochromat

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

30

rod monochromat

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

31

agnosia

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

32

anomia

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.

33

color contrast

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

34

color assimilation

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

35

unrelated color

A color that can be experienced in isolation.

36

related color

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.

37

negative afterimage

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.

38

adapting stimulus

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

39

neutral point

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.)

40

color constancy

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

41

illuminant

The light that illuminates a surface.

42

spectral reflectance function

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

43

spectral power distribution

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

44

reflectance

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.

45

absolute metrical depth cue

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).

46

accommodation

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

47

aerial perspective or haze

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.

48

anamorphosis or anamorphic projection

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.

49

Bayesian approach

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).

50

binocular

With two eyes.

51

binocular depth cue

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.

52

binocular disparity

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.

53

binocular rivalry

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

54

binocular summation

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.

55

continuity constraint

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.

56

convergence

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).

57

correspondence problem

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.

58

corresponding retinal points

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.

59

critical period

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.

60

crossed disparity

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.

61

Cyclopean

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

62

dichoptic

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.

63

diplopia

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

64

divergence

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).

65

esotropia

Strabismus in which one eye deviates inward.

66

Euclidean

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.

67

exotropia

Strabismus in which one eye deviates outward.

68

familiar size

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

69

free fusion

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

70

horopter

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

71

linear perspective

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.

72

metrical depth cue

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

73

monocular

With one eye.

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monocular depth cue

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

75

motion parallax

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.

76

nonmetrical depth cue

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).

77

occlusion

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

78

optic flow

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

79

Panum’s fusional area

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

80

pictorial depth cue

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

81

positivism

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.

82

probability summation

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

83

projective geometry

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.

84

random dot stereogram (RDS)

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.

85

realism

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

86

relative height

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.

87

relative metrical depth cue

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.

88

relative size

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

89

stereoacuity

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

90

stereoblindness

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.”

91

stereopsis

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

92

stereoscope

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.

93

strabismus

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.

94

suppression

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

95

texture gradient

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.

96

tilt aftereffect

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

97

uncrossed disparity

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.

98

uniqueness constraint

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

99

vanishing point

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

100

Vieth-Müller circle

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.