Lecture 6, Depth Perception

Question 1

The inverse problem:

Answer 1

Any retinal image is consistent with infinitely many possible configurations of the world.

Question 2

Ambiguity in Perspective:

Answer 2

Parallel lines in the world receding away from you can produce the same retinal image as converging lines that are a constant distance from you.
To interpret the image, we assume that lines in the world tend to be parallel.

Question 3

Ambiguity in Shading:

Answer 3

A convex object that is lit from above can produce the same retinal image as a concave object lit from below.
To interpret the image, we use an assumption that light comes from above.

Question 4

Ambiguity in Depth Perception:

Answer 4

Many 3D cues, particularly pictorial cues, are ambiguous.
We can overcome this ambiguity by using prior knowledge or assumptions based on physical properties of the world.
This is a type of top-down processing and supports the constructivist approach to vision.

Question 5

Ambiguity in Elevation:

Answer 5

Objects sitting on a surface can produce the same retinal image as objects floating in the air.
To interpret the image, we assume that objects rest on a ground plane.

Question 6

Erroneous Assumptions:

Answer 6

In situations where our assumptions are not valid, we will make perceptual errors.
The Ames Room and certain illusions demonstrate how erroneous assumptions can lead to incorrect perceptions.

Question 7

Integration of Multiple Cues

Answer 7

Real-world scenes have multiple cues present, which must be integrated to achieve a single unified percept.
Integration helps to overcome problems of reliability, ambiguity, and conflict.

Question 8

Types of Cue Integration

Answer 8

Three types of integration: compromise, dominance, and interaction.
Compromise: when two sources of depth information conflict, the brain will try to find a compromise between them.
Dominance: when two cues define very different shapes or depths, the brain may choose to ignore one in preference for the other.
Interaction: some cues are ambiguous, but other cues can disambiguate them.

Question 9

Compromise Integration

Answer 9

Compromise integration occurs when two cues are conflicting.
The brain will try to average them, and the final percept of shape will be biased toward the most reliable cue.

Question 10

Dominance Integration

Answer 10

Dominance integration occurs when two cues define very different shapes or depths.
The brain may choose to ignore one in preference for the other.
Large cue conflicts tend to arise when one cue’s assumptions are invalid.
Usually, the cue with valid assumptions will dominate.

Question 11

Interaction Integration

Answer 11

Interaction integration occurs when some cues are ambiguous, but other cues can disambiguate them.
Ambiguous cues, such as texture and shading, can be disambiguated by other less ambiguous cues.
Evidence suggests this stage occurs prior to cue compromise.

Question 12

Order of Integration

Answer 12

Landy et al., 1995 proposed a model of cue integration.
First, cues are disambiguated by less ambiguous cues (interaction).
Second, conflicting cues are integrated through compromise or dominance.

Question 13

Multi-Cue Integration Summary

Answer 13

Multi-cue integration helps to unify our percept of the world.
Differences in cue reliability can be resolved through compromise integration.
Large conflicts between cues can be resolved through dominance integration.
Ambiguous cues can be disambiguated through interaction integration.