Chapter 10

Question 1

Absolute disparity

Answer 1

The visual angle between the images of an object on the two retinas. When images of an object fall on corresponding points, the angle of disparity is zero. When images fall on noncorresponding points, the angle of disparity indicates the degree of noncorrespondence.

Question 2

Accretion

Answer 2

A cue that provides information about the relative depth of two surfaces. Occurs when the farther object is uncovered by the nearer object due to sideways movement of an observer relative to the objects. See also deletion.

Question 3

Active method (3-D TV)

Answer 3

A method used to create 3-D television images. The active method alternates the left-eye and right-eye images on the screen 30 or more times a second. This method is called active because the viewing glasses have a shutter system that is synchronized with the alternating images on the TV screen.

Question 4

Ames room

Answer 4

A distorted room, first built by Adelbert Ames, that creates an erroneous perception of the sizes of people in the room. The room is constructed so that two people at the far wall of the room appear to stand at the same distance from an observer. In actuality, one of the people is much farther away than the other.

Question 5

Angle of disparity

Answer 5

The visual angle between the images of an object on the two retinas. When images of an object fall on corresponding points, the angle of disparity is zero. When images fall on noncorresponding points, the angle of disparity indicates the degree of noncorrespondence.

Question 6

Angular size contrast theory

Answer 6

An explanation of the moon illusion that states that the perceived size of the moon is determined by the sizes of the objects that surround it. According to this idea, the moon appears small when it is surrounded by large objects, such as the expanse of the sky when the moon is overhead.

Question 7

Apparent distance theory

Answer 7

An explanation of the moon illusion that is based on the idea that the horizon moon, which is viewed across the filled space of the terrain, should appear farther away than the zenith moon, which is viewed through the empty space of the sky. This theory states that because the horizon and zenith moons have the same visual angle but are perceived to be at different distances, the farther appearing horizon moon should appear larger.

Question 8

Atmospheric perspective

Answer 8

A depth cue. Objects that are farther away look more blurred and bluer than objects that are closer because we must look through more air and particles to see them.

Question 9

Binocular depth cell

Answer 9

A neuron in the visual cortex that responds best to stimuli that fall on points separated by a specific degree of disparity on the two retinas. Also called a disparity-selective cell.

Question 10

Binocular disparity

Answer 10

Occurs when the retinal images of an object fall on disparate points on the two retinas.

Question 11

Binocularly fixate

Answer 11

Directing the two foveas to exactly the same spot.

Question 12

Conflicting cues theory

Answer 12

A theory of visual illusions proposed by R. H. Day, which states that our perception of line length depends on an integration of the actual line length and the overall figure length.

Question 13

Correspondence problem

Answer 13

The problem faced by the visual system, which must determine which parts of the images in the left and right eyes correspond to one another. Another way of stating the problem is: How does the visual system match up the images in the two eyes? This matching of the images is involved in determining depth perception using the cue of binocular disparity.

Question 14

Corresponding retinal points

Answer 14

The points on each retina that would overlap if one retina were slid on top of the other. Receptors at corresponding points send their signals to the same location in the brain.

Question 15

Cue approach to depth perception

Answer 15

The approach to explaining depth perception that identifies information in the retinal image, and also information provided by aiming and focusing the eyes on an object that is correlated with depth in the scene. Some of the depth cues that have been identified are overlap, relative height, relative size, atmospheric perspective, convergence, and accommodation.

Question 16

Deletion

Answer 16

A cue that provides information about the relative depth of two surfaces. Deletion occurs when a farther object is covered by a nearer object due to sideways movement of an observer relative to the objects. See also accretion.

Question 17

Disparity tuning curve

Answer 17

A plot of a neuron’s response versus the degree of disparity of a visual stimulus. The disparity to which a neuron responds best is an important property of disparity-selective cells, which are also called binocular depth cells.

Question 18

Disparity-selective cell

Answer 18

A neuron in the visual cortex that responds best to stimuli that fall on points separated by a specific degree of disparity on the two retinas. Also called a binocular depth cell.

Question 19

Echolocation

Answer 19

Locating objects by sending out high-frequency pulses and sensing the echo created when these pulses are reflected from objects in the environment. Echolocation is used by bats and dolphins.

Question 20

Emmert’s law

Answer 20

A law stating that the size of an afterimage depends on the distance of the surface against which the afterimage is viewed. The farther away the surface, the larger the afterimage appears.

Question 21

Familiar size

Answer 21

A depth cue in which judgment of distance is based on knowledge of the sizes of objects. Epstein’s coin experiment illustrated the operation of the cue of familiar size by showing that the relative sizes of the coins infl uenced perception of the coins’ distances.

Question 22

Frontal eyes

Answer 22

Eyes located in front of the head, so the views of the two eyes overlap.

Question 23

Horopter

Answer 23

An imaginary surface that passes through the point of fixation. Images caused by a visual stimulus on this surface fall on corresponding points on the two retinas.

Question 24

Lateral eyes

Answer 24

Eyes located on opposite sides of an animal’s head, so the views of the two eyes do not overlap or overlap only slightly, as in the pigeon and rabbit.

Question 25

Lenticular projection

Answer 25

A method used to create 3-D television images. The screen is coated with a film containing two sets of lenses, which results in different images reaching the left and right eyes.

Question 26

Müller-Lyer illusion

Answer 26

An illusion in which two lines of equal length appear to be of different lengths because of the addition of “fins’’ to the ends of the lines.

Question 27

Misapplied size constancy scaling

Answer 27

A principle, proposed by Richard Gregory, that when mechanisms that help maintain size constancy in the three-dimensional world are applied to two-dimensional pictures, an illusion of size sometimes results.

Question 28

Monocular cue

Answer 28

Depth cue—such as overlap, relative size, relative height, familiar size, linear perspective, movement parallax, and accommodation—that can work when we use only one eye.

Question 29

Moon illusion

Answer 29

An illusion in which the moon appears to be larger when it is on or near the horizon than when it is high in the sky.

Question 30

Motion parallax

Answer 30

A depth cue. As an observer moves, nearby objects appear to move rapidly across the visual field, whereas far objects appear to move more slowly.

Question 31

Noncorresponding points

Answer 31

Two points, one on each retina, that would not overlap if the retinas were slid onto each other. Also called disparate points.

Question 32

Occlusion

Answer 32

Depth cue in which one object hides or partially hides another object from view, causing the hidden object to be perceived as being farther away. A monocular depth cue.

Question 33

Oculomotor cue

Answer 33

Depth cue that depends on our ability to sense the position of our eyes and the tension in our eye muscles. Accommodation and convergence are oculomotor cues.

Question 34

Passive method (3-D TV)

Answer 34

A method used to create 3-D television images. Polarized light is used to create left and right images—one image is polarized so its vibration is vertical, and the other is polarized so its vibration is horizontal. The TV is viewed through polarizing lenses, which let vertically polarized light into one eye and horizontally polarized light into the other eye, creating the disparity that results in three-dimensional perception.

Question 35

Perspective convergence

Answer 35

The perception that parallel lines in the distance converge as distance increases.

Question 36

Pictorial cue

Answer 36

Monocular depth cue, such as overlap, relative height, and relative size, that can be depicted in pictures.

Question 37

Ponzo illusion

Answer 37

An illusion of size in which two objects of equal size that are positioned between two converging lines appear to be different in size. Also called the railroad track illusion.

Question 38

Random-dot stereogram

Answer 38

A pair of stereoscopic images made up of random dots. When one section of this pattern is shifted slightly in one direction, the resulting disparity causes the shifted section to appear above or below the rest of the pattern when the patterns are viewed in a stereoscope.

Question 39

Relative disparity

Answer 39

The difference between two objects’ absolute disparities.

Question 40

Relative height

Answer 40

A monocular depth cue. Objects that have bases below the horizon appear to be farther away when they are higher in the field of view. Objects that have bases above the horizon appear to be farther away when they are lower in the field of view.

Question 41

Relative size

Answer 41

A cue for depth perception. When two objects are of equal size, the one that is farther away will take up less of the field of view.

Question 42

Size constancy

Answer 42

Occurs when the size of an object is perceived to remain the same even when it is viewed from different distances.

Question 43

Size-distance scaling

Answer 43

A hypothesized mechanism that helps maintain size constancy by taking an object’s perceived distance into account. According to this mechanism, an object’s perceived size, S, is determined by multiplying the size of the retinal image, R, times the object’s perceived distance, D.

Question 44

Stereopsis

Answer 44

The impression of depth that results from binocular disparity—the difference in the position of images of the same object on the retinas of the two eyes.

Question 45

Stereoscope

Answer 45

A device that presents pictures to the left and the right eyes so that the binocular disparity a person would experience when viewing an actual scene is duplicated. The result is a convincing illusion of depth.

Question 46

Stereoscopic depth perception

Answer 46

The perception of depth that is created by input from both eyes. See also binocular disparity.

Question 47

Stereoscopic vision

Answer 47

Two-eyed depth perception involving mechanisms that take into account differences in the images formed on the left and right eyes.

Question 48

Strabismus

Answer 48

Misalignment of the eyes, such as crossed-eyes or walleyes (outward looking eyes), in which the visual system suppresses vision in one of the eyes to avoid double vision, so the person sees the world with only one eye at a time.

Question 49

Texture gradient

Answer 49

The visual pattern formed by a regularly textured surface that extends away from the observer. This pattern provides information for distance because the elements in a texture gradient appear smaller as distance from the observer increases.

Question 50

Visual angle

Answer 50

The angle of an object relative to an observer’s eyes. This angle can be determined by extending two lines from the eye—one to one end of an object and the other to the other end of the object. Because an object’s visual angle is always determined relative to an observer, its visual angle changes as the distance between the object and the observer changes.