10: Perceiving Depth & Size

Question 1

What are the three depth cues?

Answer 1

Oculomotor Cues: sensation of eye position, and accommodation.

Monocular Cues: require only one eye.

Binocular Cues: depend on two eyes.

Question 2

In oculomotor cues, what is convergence?

Answer 2

Feel the inward movement of our eyes (proprioception).

Question 3

In oculomotor cues, what is accommodation?

Answer 3

Sense the contraction of the ciliary bodies.

Question 4

In monocular cues, what is occlusion?

Answer 4

When one object hides another object, the hidden object is perceived as farther away.

Question 5

In monocular cues, what is relative height?

Answer 5

Below the horizon: higher objects are farther away.

Above the horizon: lower objects are farther away.

Question 6

In monocular cues, what is familiar size?

Answer 6

Helps in judging distance based on prior knowledge of the size of objects.

Question 7

Studies by Epstein (1965) found what about familiar size?

Answer 7

Dark room, coins illuminated by spotlight - dime: close; nickel: far; quarter: farthest.

Light room: Oddly sized coins all at the same distance.

Question 8

In monocular cues, what is relative size?

Answer 8

When two objects are of equal size, the farther object will take up less of your field of view.

Question 9

In monocular cues, what is perspective convergence?

Answer 9

Parallel lines converge as distance increases.

Question 10

In monocular cues, what is atmospheric perspective?

Answer 10

Air filters and scatters light, distant objects appear less sharp (lower contrast) and tinted blue.

Question 11

In monocular cues, what is texture gradient?

Answer 11

Textures appear more closely packed as distance increases.

Question 12

In monocular cues, what pieces of information can shadows provide?

Answer 12

Can provide cues about the position of the light source and also depth within the image.

Enhance 3D appearance of objects.

Question 13

How does motion work for monocular cues?

Answer 13

Pictorial depth cues work when the observer is stationary. When the observer moves, even more depth cues are available.

Question 14

In monocular cues for motion, what is motion parallax?

Answer 14

When an observer moves, objects nearer the observer move faster than more distant objects.

Question 15

When you are a moving observer and fixate on an object, the object is _____, other stuff that is closer moves _____, other stuff that is farther moves _____.

Answer 15

Stationary; in opposite direction as observer; in same direction as observer.

Question 16

When you are a moving observer, objects farther from the fixation _____.

Answer 16

Move faster.

Question 17

What is deletion? Accretion?

Answer 17

Deletion: gradual occlusion of a moving object as it passes behind another object.

Accretion: gradual reappearance of a moving object as it emerges from behind another object.

Question 18

What is binocular disparity?

Answer 18

Difference in images in the right and left eyes.

Question 19

What is the horopter? How does it cast images onto the retina? Is there any disparity?

Answer 19

Imaginary border.

Cast images onto the retina that have corresponding points on the retina.

Zero disparity.

Question 20

Images of objects not on the horopter fall on _____ on the retina. The farther away from the horopter, the greater the _____.

Answer 20

Non-corresponding points; angle of disparity.

Question 21

Things behind the horopter are in _____ disparity. Things in front are in _____ disparity.

Answer 21

Uncrossed; crossed.

Question 22

Explain relative vs. absolute disparity.

Answer 22

Absolute disparity will change as fixation points change. Relative disparity is the difference in 2 objects’ absolute disparities.

Question 23

Impression of depth from binocular disparity information is what?

Answer 23

Stereopsis.

Question 24

Disparity, a _____ element, creates steropsis, a _____ element.

Answer 24

Geometrical; perceptual.

Question 25

What alone is sufficient to create the perception of depth?

Answer 25

Retinal disparity.

Question 26

What is the correspondence problem?

Answer 26

How does the visual system match the parts of the images in the left and right eyes that correspond with each other?

Question 27

In autostereograms, there is disparity in a single image. But if you diverge your gaze, while still focusing on the image, what happens?

Answer 27

Some dots fall on non-corresponding points on the retinas.

Question 28

Available depth cues depend on what two things?

Answer 28

Eye placement (frontal vs. lateral).

Head size (inter-ocular distance).

Question 29

Some species use non-visual cues to determine depth. What do bats use? Electric fish?

Answer 29

Bats: echolocation.

Electric fish: electrolocation.

Question 30

Some binocular neurons in _____ are disparity specific.

Answer 30

V1.

Question 31

Along what stream do neurons mostly respond to absolute depth? What actions do they likely play a role in?

Answer 31

Dorsal stream.

Grasping, reaching.

Question 32

Along what stream do neurons mostly respond to relative depth? What function does this have?

Answer 32

Ventral stream.

Support object/shape perception.

Question 33

What happened when kittens were raised for 6 months with only monocular vision (left or right eye patched on alternated days)?

Answer 33

Very few binocular neurons in V1, could not use stereopsis information for behavioural tasks.

Question 34

What happened in microstimulation studies where monkeys were trained to make stereoscopic depth judgments?

Answer 34

Small electrical current passed through a “depth column” in middle temporal cortex. Monkey’s behavioural report of perceived depth is skewed towards the stimulated depth.

Question 35

Perceived depth and size of objects must be what?

Answer 35

Codependent.

Question 36

If two objects are perceived at the same distance, then they must be _____. If one is perceived as larger, then it must be _____.

Answer 36

The same size; farther away from the other.

Question 37

What is size constancy? How can we do it?

Answer 37

Perceive an object’s physical size irrespective of its distance from us.

Can do this because of depth information, size-distance scaling mechanism.

Question 38

What is the equation for size-distance scaling? Which variables are affected by depth cues?

Answer 38

Sp = Sr x Dp

Sp = perceived size
Sr = retinal image size
Dp = perceived distance

Sp and Dp affected by depth cues.

Question 39

What is Emmert’s Law?

Answer 39

The farther away an afterimage appears, the larger its size.

Question 40

Without depth cues (e.g. whiteout), size can be _____.

Answer 40

Misinterpreted.

Question 41

Other depth cues provide additional size information. What do relative size and texture show?

Answer 41

Relative size: familiar objects can act as a “yardstick” for unfamiliar objects.

Texture: creates impression/outline of objects; distinguishes objects.

Question 42

What is veridical perception? In what environments are human depth and size perception close to veridical?

Answer 42

Perception that matches the actual physical stimulus.

Well-lit natural environments.

Question 43

The Muller-Lyer illusion plays into what two cues?

Answer 43

Misapplies size constancy scaling; conflicting cues.

Question 44

What is the Ames room?

Answer 44

Designed so that monocular depth cues give the illusion that two people (or L/R corners of the room) are equally far away.

Question 45

What is required to design an Ames room?

Answer 45

Six-sided convex polyhedron: depending on the design of the room, all surfaces can be trapezia.

Question 46

The horizon moon is perceived as farther away, and therefore larger in the apparent distance (flattened heavens) theory. The elevated moon is perceived as closer, and therefore smaller. Why is this?

Answer 46

Horizon moon: many depth cues from terrain and surface objects.

Elevated moon: few depth cues.

Question 47

What is the angular-size contrast theory in relation to the apparent distance theory?

Answer 47

Moon appears smaller when surrounded by larger objects.