19. conflicting depth cues

Question 1

What does the perceptual system do when there are conflicting depth cues? What usually happens?

Answer 1

• perceptual system assumes ALL cues are right
• tries to figure out what could be going on in the world to make the depth cues reasonable
• often can lead to illusions

Question 2

4 types of illusions caused by resolution of conflicting depth cues?

Answer 2

1. Hollow mask
2. Arch illusion
3. Anaglyph movement
4. Ames window (rotating trapezoid)

Question 3

Hollow mask illusion –> What is it? What do you perceive? (How is it ultimately resolved)

Answer 3

• you’re looking at a hollow mask
• you perceive a normal protruding face, but when you move, it turns to follow you

Question 4

Hollow mask illusion –> what depth cues are there? Which are wrong vs. right?

Answer 4

Wrong:
1. Familiarity with faces –> assume nose is close
2. Shape from shading –> hollow mask lit from below puts highlight on forehead, which is how a protruding face lit from above would appear

Right:
1. motion parallax –> the nose is farthest, so it moves slower than the other aspects that are closer

Question 5

Arch illusion –> what is it? What COULD someone perceive?

Answer 5

• St. louis arch is shown with limited AMBIGUOUS depth information
• top of the arch is cut off
• people are equally likely to perceive either “leg” as closest

Question 6

Arch illusion –> if you were moving in a helicopter, with limited depth information, and the top of the arch occluded, what COULD you see?

Answer 6

• like the hollow face illusion, IF you perceived the depth INCORRECTLY originally, you’d perceive motion in the opposite direction

Question 7

Anaglyph movement illusion –> what is it? ex from class? what depth cue is wrong vs right?

Answer 7

• binocular disparity gives illusion of depth (some words look closer than others)
  –> disparity is wrong!
  –> diff. colors adjusted 6cm apart
• motion parallax info (right) tells you that none of the words are actually closer
• you PERCEIVE some of the words as MOVING

ex. “REAL 3D” in red and yellow

Question 8

Ames window (rotating trapezoid w/pen) –> what is it? what depth cues are right vs wrong? what do you perceive?

Answer 8

• trapezoidal window (one side smaller than the other) with pen attached sticking through the window
• Wrong: linear perspective and relative size
  –> you think shorter segment is always further away
• Right: motion parallax (caused by object moving)
• you perceive the window as flip flopping, while the pen is fully rotating and moving “through” the window (resolution)

Question 9

In all illusions with conflicting depth cues, what was the 2nd cue, which was correct/reliable?

Answer 9

• motion parallax