Topic 10: Depth & Size Perception

Question 1

Cue Approach to Depth Perception

Answer 1

the approach to explaining depth perception that focuses on identifying information in the retinal image 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 2

Occlusion

Answer 2

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 3

Oculomotor Cues

Answer 3

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 4

Monocular Cues

Answer 4

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 5

Pictorial Cues

Answer 5

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

Question 6

Relative Height

Answer 6

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 7

Familiar Size

Answer 7

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 size of coins influenced perception of the coin’s distances

Question 8

Relative Size

Answer 8

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 9

Perspective Convergence

Answer 9

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

Question 10

Atmospheric Perspective

Answer 10

a depth cue

objects that are farther away look more blurred and bluer than objects that are closer because we look through more air and particles to see them

Question 11

Texture Gradient

Answer 11

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 12

Motion Parallax

Answer 12

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 13

Deletion

Answer 13

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

Question 14

Accretion

Answer 14

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

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

Question 15

Stereoscopic Vision

Answer 15

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

Question 16

Stereoscopic Depth Perception

Answer 16

the perception of depth that is created by input from both eyes

Question 17

Strabismus

Answer 17

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 18

Binocular Disparity

Answer 18

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

Question 19

Corresponding Retinal Points

Answer 19

the points on each retina that would overlap if one retina were slid on top of the other

receptors at corresponding point send their signals to the same location in the brain

Question 20

Horopter

Answer 20

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 21

Noncorresponding Points

Answer 21

two points, one on each retina, that would not overlap if the retinas were slid onto each other

also called disparate points

Question 22

Absolute Disparity

Answer 22

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 noncorrespondance

Question 23

Angle of Disparity

Answer 23

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 24

Crossed Disparity

Answer 24

disparity that occurs when one object is being fixated, and is therefore on the horopter, and another object is located in front of the horopter, closer to the observer

Question 25

Uncrossed Disparity

Answer 25

disparity that occurs when one object is being fixated, and is therefore on the horopter, and another object is located behind the horopter, farther from the observer

Question 26

Relative Disparity

Answer 26

the difference between two objects’ absolute disparities

Question 27

Stereopsis

Answer 27

the impression of depth that results from binocular disparity

the differences in the position of images of the same object on the retinas of the two eyes

Question 28

Random-Dot Stereogram

Answer 28

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 29

Stereoscope

Answer 29

a device that presents pictures to the left and 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 30

Correspondence Problem

Answer 30

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 we of binocular disparity

Question 31

Binocular Depth Cells

Answer 31

a neuron in the visual cortex that responds best to stimuli that fall on points separated by a specific degree of disparity on teh two retinas

also called a disparity-selective cell

Question 32

Disparity Turning Curve

Answer 32

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 cell, which are also called binocular depth cells

Question 33

Frontal Eyes

Answer 33

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

Question 34

Lateral Eyes

Answer 34

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

Question 35

Echolocation

Answer 35

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 36

Visual Angle

Answer 36

the angle of an object relative to an observer’s eyes

this angle can be determined by expanding two lines from the eye, one to one end of an object

because an object’s visual angle is always determined relative to an observer, it’s visual angle changes as the distance between the object and observer changes

Question 37

Size Constancy

Answer 37

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

Question 38

Size-Distance Scaling

Answer 38

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, by the object’s perceived distance, D

Question 39

Emmert’s Law

Answer 39

a law stating that the size of an afterimage depends on teh distance of the surface against which the afterimage is viewed

the farther away the surface, the larger the afterimage appears

Question 40

Muller-Lyer Illusion

Answer 40

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 41

Misapplied Size Constancy Scaling

Answer 41

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, and illusion of size sometimes results

Question 42

Conflicting Cues Theory

Answer 42

a theory of visual illusion 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 43

Ponzo Illusion

Answer 43

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 44

Ames Room

Answer 44

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 45

Moon Illusion

Answer 45

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 46

Apparent Distance Theory

Answer 46

an explanation of the moon illusion that is based on teh idea that the horizon moon, which is viewed across the filled space of teh 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 moon have the same visual angle but are perceived to be at different distances, the farther appearing horizon moon should appear larger

Question 47

Angular Size Contrast Theory

Answer 47

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 48

Binocularly Fixate

Answer 48

directing two fovea’s to exactly the same spot

Question 49

What is absolute distance judgment?

Answer 49

“egocentric” localization (you <–> object)

Question 50

What is relative distance judgment?

Answer 50

requires object-relative localization (object <–> object)

Question 51

What is occlusion?

Answer 51

if object A covers part of object B, then A is seen as closer than B

Question 52

What is shading and shadows?

Answer 52

indicates which surfaces are facing the light source and which are not

Question 53

What is atmospheric perspective?

Answer 53

greater absolute distance makes objects appear fuzzier, bluer

Leonardo da Vinci suggested application in painting (“thus if one is to be five times as distant, make it fives time bluer”)

Question 54

What is relative size?

Answer 54

same size object farther away produces smaller visual angle

Question 55

What is familiar size?

Answer 55

knowledge of object’s actual size influences perception of its distance

Question 56

What is linear perspective?

Answer 56

apparent convergence of receding parallel lines at a vanishing point

Question 57

What is relative height?

Answer 57

below the horizon, higher objects appear farther away; above the horizon, lower objects appear farther

Question 58

What is texture gradient?

Answer 58

texture elements appear smaller and more densely arranged as they get farther away

higher-order depth cue: made up of linear perspective + relative size

Question 59

What are pictorial depth cues?

Answer 59

occlusion
shading & shadows
atmospheric perspective
relative size
familiar size
linear perspective
relative height
texture gradient

Question 60

What are motion-based depth cues?

Answer 60

motion parallax
deletion
accretion

Question 61

What is motion parallax?

Answer 61

as observer moves perpendicular object (side-to-side), nearby objects appear to move past more rapidly than faraway objects

Question 62

What is deletion?

Answer 62

background object is occluded by foreground object moving in front of it

Question 63

What is accretion?

Answer 63

background object is uncovered by foreground object moving out of the way

Question 64

What is accommodation?

Answer 64

crystalline lens changes shape to focus on objects

feedback from ciliary muscles provides information on lens curvature, and therefore distance

Question 65

What is convergence?

Answer 65

rotation of eyes inward to cause image to fall on the fovea

smaller convergence angle = farther object; larger angle = closer

Question 66

What is the interaction of depth cues?

Answer 66

depth cues rarely used alone; most used in conjunction with others

accuracy in estimating distance is an additive relation between depth cues

also, perception of depth is stronger with more cues

Question 67

What is binocular (or retinal) disparity?

Answer 67

retinal images of an object fall on disparate points on each eye’s retina

Question 68

What is stereopsis?

Answer 68

perception of depth based on retinal disparity alone

Question 69

What is horopter?

Answer 69

imaginary surface passing through fixation point

is a distal stimulus lies on the horopter, then the proximal stimulus will fall on corresponding points on each retina (no disparity)

if a distal stimulus is not on the horopter, then the proximal stimulus produces disparity

the distance between points on each retina is called the degree (or angle) of disparity

the farther from the horopter, the greater disparity

Question 70

What are random-dot stereograms?

Answer 70

each eye sees the same pattern of random dots, with one exception

central region in each pattern is shifted over; this creates retinal disparity

shifted region is perceived as floating above the background

Question 71

What are single-image random-dot stereograms?

Answer 71

retinal disparity in “autostereograms” is produced in opposite way from random-dot stereograms

usually, two slightly different images are directed onto the same part of each retina

in SIRDSs, a single image is observed so that it falls on two different parts of each retina

Question 72

What are the steps of viewing an autostereogram?

Answer 72

1. have a small angle of convergence (e.g., look at a wall or distant object)
2. look at autostereogram, but don’t change convergence; you should see two overlapping images
3. change accommodation to bring images into focus, keeping convergence constant
4. change convergence until repeating parts of the pattern line up horizontally

Question 73

What is the correspondence problem?

Answer 73

how is it determined which dots (or visual features) in the left eye match with after dots (or visual features) in the right eye, to fuse the two images into one percept?

Question 74

What are the proposed solutions to the correspondence problem?

Answer 74

matches are made only between elements that are similar (e.g., a black dot in the left eye can only match a black dot in the right eye)

however, no widely accepted solution has been created yet

Question 75

What are the sensitive/critical periods in the development of depth perception?

Answer 75

in humans, binocular depth develops early: 3-5 months

collision info apparent as young as 2-3 weeks

pictorial depth cues used later: 6-7 months

depth information from shadows may not appear until ~3 years

Question 76

What was the Holway & Boring size perception experiment?

Answer 76

task: adjust size of comparison circle to match that of various sized test circles, placed at different distances

visual angle of all test circles is one degree (same retinal size or visual angle)

normal viewing: if test circle was large (and far), observers chose large comparisons, too

depth cues eliminated: observers looked at test circles with one eye through a peephole

all stimuli had the same visual angle, so the size of the comparison matched the visual angle of the test circle, not the size of the test circle

Question 77

What is size constancy?

Answer 77

as distance from a given object increases, retinal image becomes smaller, yet we do not perceive the object as getting smaller

distance taken into account when perceiving size: size-distance scaling

distance & depth cues (pictorial, accommodation, convergence, disparity) must be available, or errors will occur

illusions are often caused by misapplied size constancy (generally exist on paper; are rare in the real world)

Question 78

What is the Muller-Lyer Illusion?

Answer 78

illusion is weaker in children and in people living in dome-shaped huts

“carpentered world” hypothesis: (a) like inside corner of a room, (b) like outside edge of a building

depth cues indicate (a) is relatively far away, (b) is relatively close

due to size constancy, (a) appears longer, (b) appears shorter

Question 79

What is the moon illusion?

Answer 79

horizon moon seems to be much larger than zenith (overhead) moon

but moon’s retinal size, and actual distance are essentially constant

misjudgment of moon’s size is an illusion, resulting from a misperception of distance

if an object perceived to be (or actually) farther away has the same visual angle as an object perceived to be (or actually) nearer, the farther object will appear larger

Question 80

What is the apparent-distance theory?

Answer 80

objects on the horizon, viewed across the filled space of the terrain, should appear to be farther away

objects at the zenith, seen through the empty space of the sky, should appear to be closer

Question 81

What was Boring’s solution to the moon illusion?

Answer 81

eye elevation hypothesis: moving eyes upwards makes objects appear smaller

Question 82

What is Emmert’s Law?

Answer 82

perceived size of an object having a constant visual angle is proportional to the (perceived) distance of the object

Question 83

What was the solution to the moon illusion based on Claudius Ptolemy?

Answer 83

plants were objects that moved on sets of transparent heavenly spheres

“vault of the heavens” is flattened

the moon seems to travel along a flat sky

horizon appears farther away

result: zenith moon appears closer than horizon moon, due to size constancy its apparent size is thus smaller