Three Dimensions

Question 1

monocular vision

Answer 1

one-eyed vision

Question 2

binocular vision

Answer 2

two-eyed vision

Question 3

visual field

Answer 3

visual field of a human is limited ~190° horizontally, 110° of which is covered by both eyes

Question 4

binocular summation

Answer 4

the combination of signals from both eyes that makes performance on many tasks better than with either eye alone. Binocular vision makes the probability to detect small, fast-moving objects much higher, because there are 2 “detectors” looking for the object

Question 5

Oculomotor cues

Answer 5

cues based on our ability to sense the position of our eyes and the tension in our eyes muscles. Oculomotor cues are created by convergence and accommodation

Question 6

Convergence

Answer 6

the inward movement of the eyes that occurs when we look at nearby objects

Question 7

Accomodation

Answer 7

the change in the shape of the lens that occurs when we focus on objects at various distances. We can feel the inward movement of the eyes during convergence and the tightening of eye muscles during accommodation. The feeling itself is the cue

Question 8

Monocular depth cue

Answer 8

a depth cue that is availabe even when the world is viewed with one eye only. Accomodation is a monocular depth cue.

Question 9

Pictorial depth cue

Answer 9

a depth cue that can be depicted in a 2D picture

Question 10

Occlusion

Answer 10

a depth cue in which one object obstruct the view of (part of) another object. Occlusion is reliable in almost all cases, with the exception of accidental viewpoints

Question 11

nonmetrical depth cue

Answer 11

it provides information about depth order, but not about depth magnitude (i.e., it does not provide information about distance between the occluders and occludees)

Question 12

relative height

Answer 12

objects on the ground that are higher in the field of view appear farther away. Objects in the skay that are lower in the field of view appear farther away

Question 13

familiar size

Answer 13

judging distance based on prior knowledge of object sizes

Question 14

relative size

Answer 14

when 2 objects are known to be of equal physical size, the one that is farther away will appear smaller

Question 15

Perspective convergence (linear perspective)

Answer 15

parallel lines converge in the distance

Question 16

atmospheric/aerial/haze perspective

Answer 16

distant objects appear less sharp than nearer objects and sometimes have a slight blue tint. This occurs because the farther away an object is, the more air and particles we have to look through. The blue tint is due to the fact that the atmosphere preferentially scatters short-wavelength light, which appears blue

Question 17

texture gradient

Answer 17

when a number of similar objects are equally spaced throughout a scene, they create a texture gradient. This results in a perception of depth: we see the more closely spaced elements farther away.

Question 18

shadows

Answer 18

decreases in light intensity caused by the blockage of light- can provide information about the location of objects. Shadows also enhance the three-dimensionality of objects

Question 19

motion-produced cues

Answer 19

depth cues that emerge when the observer is moving and enhance depth perception

Question 20

motion parallax

Answer 20

as we move, nearby objects appear to glide rapidly past us, but more distant objects appear to move more slowly. The reason is that moving the eye from one point to another while looking at a closer object causes its retinal image to move more than that of a more distance object

Question 21

deletion and accretion

Answer 21

as an observer moves sideways, some things become covered (deletion) and other become uncovered (accretion)

Question 22

binocular disparity

Answer 22

the 2 retinas receive a slightly different visual image of the same scene due to the different positions of the eyes. The visual system reconstructs a 3-D world based on the inverted (slightly different) 2-D images of the world on the retina

Question 23

corresponding retinal points

Answer 23

points on the retina that would overlap if the eyes were superimposed on each other

Question 24

horopter

Answer 24

a surface in the world on which all points fall on corresponding retinal points

Question 25

noncorresponding points

Answer 25

the images of objects that are not on the horopter fall on noncorresponding points

Question 26

absolute disparity

Answer 26

the degree to which e.g., Bill’s image deviates from falling on corresponding points. Measured with an angle of disparity

Question 27

angle of disparity

Answer 27

the angle between the corresponding point on the right eye for the left-eye image of bill and the actualy location of the image on the right eye

Question 28

crossed disparity

Answer 28

an object that is closer to the observer than his/her fixation point (in front of the horopter) is seen to the right of fixation point by the left eye and to the left of fixation point by right eye

Question 29

uncrossed disparity

Answer 29

the left eye sees an object to the left of the observer’s fixation point and the right eye sees the same object to the right of the fixation point. Occurs when an object is behind the horopter

Question 30

stereopsis

Answer 30

depth perception that results from information provided by binocular disparity. Stereopsis is not necessary for 3D vision, but adds richness to the perception of the 3D world

Question 31

random-dot stereogram

Answer 31

a stimulus that contains no depth cues other than disparity. It consists of 2 images of random-dot patterns, which are identical except for a square region from one of the patterns moved to the side

Question 32

the correspondence problem

Answer 32

the visual system needs to solve the problem of matching every bit of the image in the left eye to bit in the right eye. It is not yet known how this happens

Question 33

uniqueness constraint

Answer 33

a feature in the world is represented exactly once in each retinal image -> each monocular image feature should be paired with exactly one feature in the other monocular image

Question 34

continuity constraint

Answer 34

except at the edges of objects, neighboring points in the world lie at similar distances from the viewer -> disparity chould change smoothly at most places in the image

Question 35

binocular depth cells (or disparity-selective cells)

Answer 35

neurons that respond best when stimuli presented to the left and right eyes create a specific amount of absolute disparity. Disparity-selective neurons appear in most of the visual cortex and parts of the parietal cortex

Question 36

disparity tuning curve

Answer 36

indicates the neural response that occues when stimuli create different amounts of disparity

Question 37

role of V2

Answer 37

involved in computing depth order based on contour completion and border ownership processes

Question 38

V4

Answer 38

encode depth intervals based on relative disparities

Question 39

IT cortex and other higher cortical areas

Answer 39

involved in the representation of complex 3D shapes

Question 40

visual angle

Answer 40

the angle of an object relative to the observer’s eye. The visual angle depends both on the size of the stimulus and on its distance from the observer -> a small near object can have the same visual angle as a far larger object. The visual angle says how lage an object will be on the retina

Question 41

size constancy

Answer 41

our perception of an object’s size is relatively constant even when we view the object from different distances (and thus the visual angle gets smaller)

Question 42

Size-distance scaling

Answer 42

a proposed mechanism for how size constancy works. It is expressed by the formula S = K(R x D)
S = an object’s perceived size
K = a constant
R = the size of the retinal image of the object
D = the perceived distance from the object

Question 43

Muller-Lyer illusion

Answer 43

the right vertical line in the figure appears to be longer than the left vertical line, even though their length is equal

Question 44

Misapplied size constancy scaling

Answer 44

a mechanism that explains the Muller-Lyer illusion.

Question 45

Conflicting cues theory

Answer 45

our perception of line length depends on 2 cues:
1. The actual length of the line
2. The overall length of the figure
-> the overall length of the right figure is bigger than the overall of the left figure, which is why the illusion could be perceived

Question 46

the ponzo (railroad track) illusion

Answer 46

both animals in the figure have the same visual angle, but the one on top appears longer. Misapplied size constancy scaling explanation -> the top animal appeaers bigger because of depth information provided by converging railroad tracks

Question 47

moon illusion

Answer 47

when the moon is on the horizon it appears much larger then when it is high in the sky. However, the visual angles of the horizon moon and the elevated moon are the same

Question 48

Apparent distance theory

Answer 48

the moon on the horizon appears more distant because it is viewed across the filled space of the terrain, which contains depth information. Since S = R x D and R is constant here, but D increases for the horizon moon, S for the horizon moon is larger

Question 49

Angular size contrast theory

Answer 49

the elevated moon appears smaller because the large expanse of sky surrounding it makes it appear smaller by comparison

Question 50

Study with cats

Answer 50

Cats were reared so that their vision was alternated between left and right eyes every other day during the first 6 months of their lives.
-> After the 6-month period, the cats had fewer binocular neurons
-> cats also performed poorly on a depth perception task
-> Disparity-selective neurons appear in most of the visual cortex and parts of the parietal cortex

Question 51

Holway and Boring’s experiment

Answer 51

A person has to adjust the size of a comparison circle to be the same as the size of a test circle, whose distance is being changed, but retinal size stays constant.
-> When all depth cues are available, people tend to judge size correctly. They make the comparison circle small when the test circle is close and they make it large when the test circle is far away.
-> When depth cues are eliminated 1 by 1, the judgments of size become less accurate
-> When all depth information is eliminated, the observer’s perception of size is determined by the visual angles of the circle’s images on the retinas.