Chapter 10: Percieving Depth and Size

Question 1

What is the cue approach to depth perception?

Answer 1

We have specific information (cues) in the retinal image that we correlate to the depth in the scene. We learn this connection between cue and depth through experience.

Question 2

What are the three categories of cues?

Answer 2

Oculomotor: based on eye position and muscle tension
Monocular: one eye based cues
Binocular: two eye based cues

Question 3

What are the two oculomotor cues?

Answer 3

Convergence: sensing the inward motion of our eyes when looking at close up objects

Accommodation: the change in lens shape by our cilliary muscles when looking at far off objects.

Question 4

What is occlusion

Answer 4

When one object is partially covered by another. It tells you which object is in front but does not tell you about the distance between them.

Question 5

what is Relative height?

Answer 5

Using an objects location relative to the horizan line to interpret how close or far away they are. Objects closer to the horizon line tend to be farther away.

Question 6

What is familiar and relative size?

Answer 6

Familiar size: judging distance based on our prior knowledge of the sizes of objects.

Relative size: when two objects are known to be the same size but one appears smaller than the other, we judge the smaller one to be farther away.

Question 7

What is perspective convergence?

Answer 7

Perspective convergence: when parallel lines appear to converge as they move farther away

Question 8

What is atmospheric perspective?

Answer 8

the farther away an object, the more air particles we have to look through to see it, resulting in further away objects having a fuzzy and bluish tinge.

Question 9

What is texture gradient?

Answer 9

When a number of similar objects are equally spaced throughout a scene, they appear to be closer together as they move farther away.

Question 10

What are shadows as monocular cues?

Answer 10

shadows tell us information about an objects location and enhance the 3 dimensionality of an object.

Question 11

what is the motion parallax?

Answer 11

as we move, near by objects appear to guide rapidly past us but more distant objects appear to move more slowly.

Question 12

What is deletion and accretion?

Answer 12

As we move sideways, some things become covered and others uncovered.

Question 13

What is stereoscopic depth perception and how does binocular information lead to it.

Answer 13

Stereoscopic depth information is depth perception created from input from both eyes. The basis of this stereoscopic vision is accounting for the differences in the images formed on the left and right retina.

Question 14

What is binocular disparity and how does it relate to the ideas of corresponding and non-corresponding points?

Answer 14

Binocular disparity is the difference in the images on the left and right retina. Images on the retina can either be corresponding points in that the points would overlap if the eyes were superimposed on each other, or they can be non-corresponding in that they do not overlap.

Absolute disparity is the degree to which the points on the each retina deviate. Higher absolute disparity is equatable to higher distance from the horopter.

Question 15

What is the horopter?

Answer 15

The horopter is an imaginary line curved through the field of vision based on where the person is looking directly.

Points that fall on the horopter are corresponding points and points that fall off the horopter are non-corresponding points.

Question 16

What is crossed and uncrossed disparity? Under what conditions do they each occur?

Answer 16

Crossed Disparity: when the left eye sees the object to the right of the fixation point and the right eye sees the object to the left of the fixation point. This occurs when an object is CLOSER than the horopter.

Uncrossed Disparity: when the left eye sees the object to the left of the fixation point and the right eye sees the object to the right of the fixation point. This occurs when an object is FARTHER than the horopter.

Question 17

What is the correspondence problem and how is it explained?

Answer 17

The correspondence problem asks how the visual system is able to match the parts of images in the left and right eye that correspond to each other.

This is a yet unsolved problem, we don’t have a clear explanation. Some thoughts are that we may be making matches by looking for specific features on objects but this does not work in all cases (e.g. random dot stereograms)

Question 18

What are binocular depth cells and where are they located?

Answer 18

Binocular depth cells are also called disparity selective cells. They are neurons that signal different amounts of disparity.

These cells are found both in and beyond area V1 (striate cortex).

Question 19

Do all animals have binocular depth?

Answer 19

No, only animals with frontal eyes (e.g. cats, monkeys etc.) use binocular disparity for depth information. Animals with sideways facing eyes have evolved to have a wider field of vision at the expense of binocular depth (e.g. rabbits).

Question 20

How do we perceive size?

Answer 20

The visual angle is an objects angle relative to the observers eye. small objects near the eye can have the same visual angle as large objects far away.

We combine information from the visual angle with depth cues to perceive size.

We also use cues like the size of nearby objects, previous knowledge, and texture gradient to perceive size.

Question 21

What is size constancy?

Answer 21

The fact that our perception of an objects size is relatively constant even when viewed from different distances. Size constancy works even under conditions of poor depth perception.

Question 22

What is the Muller Lyer Illusion and what are two possible explanations.

Answer 22

It is two lines placed side by side with two points either expanding at the top or narrowing (like an arrow). This illusion makes you see the line with the expanding top as longer than the line with the narrowing top despite them being the exact same length

Why? One proposal is that we are misapplying size constancy scaling and using 3D principles if depth on a 2D image. Essentially we are viewing them inward and outward corners and think that, despite looking the same length, the inward corner must be farther away therefore it is actually longer.

This answer has been challenged. (e.g. the dumbbell version and the 3D display version don’t work with this explanation.

Second explanation: Conflicting cues theory: we are trying to reconcile the actual length of the single line with the overall length of the object. These to conflicting cues are integrated into a compromised perception of the length.

Question 23

What is Emmert’s Law?

Answer 23

Retinal size of an afterimage remains constant but perceived size will change depending on the distance of the projection.