Lec 7 Binocular Depth

Question 1

Non-pictorial cues to depth

Answer 1

1. Motion Parallax (Visual) 2. Accommodation (oculomotor) 3. Convergence (oculomotor) 4. Corresponding points and disparity 5. Stereopsis: Depth from disparity 6. Stereograms 7. Physiology

Question 2

Motion parallax

Answer 2

objects closer move slower; objects further move faster

Question 3

Accommodation

Answer 3

-Bring a target into focus -Lens is stretched or relaxed -The visual system senses the degree of strain on the lens -Translates this into a distance for the object

Question 4

Convergence

Answer 4

the angle of convergence of the eyes=> estimate distance of object. Far objects => less convergence, smaller angle close objects => more convergence, larger angle Descartes- convergence is the primary binocular depth cue

Question 5

binocular disparity

Answer 5

difference in separation of two images in two eyes disparity= distance

Question 6

Horopter

Answer 6

locus of all points in 3-D space that fall on corresponding retinal points All points in the 3D world that have zero disparity.

Question 7

corresponding retinal points

Answer 7

same position on each retina with respect to the point of fixation (fovea)

Question 8

if the object does not fall on a horopter?

Answer 8

Angle r- Angle L= disparity

there is disparity between the two images in the two eyes

disparity indicates depth

closer = crossed disparity

further = uncrossed disparity

Question 9

Types of disparities

Answer 9

Points of fixation v

• Uncrossed disparity: object further than fixation (nasal side of eye)
• Fixating here
• Crossed disparity: object closer than fixation (non-nasal side of eye)

Question 10

Stereo Methods (3D)

Answer 10

• Red/ green glasses method
  
  • Red blocks red information from left eye
  • green blocks green information from eyes
  • dizzy from conflicting
• Brewster stereoscope
• free fusion, w/o optical aids

Question 11

Summary

Answer 11

• Motion parallax
• Accommodation and convergence
• Corresponding points and binocular disparity
• Discover shape first then disparity?
• No, disparity then shape: random dot
• stereograms
• Binocular cells with varying RF separations
• provide a neural account of stereopsis
• Binocular rivalry when image points don’t match

Question 12

Stereopsis

Answer 12

percept of depth from binocular disparity

Question 13

How does stereopsis work?

Answer 13

• match fragments from each eye and then measure binocular disparity? NO
• Requires object recognition?- NOPE. Proof: random dot stereograms in which you can see depth in the dot stereograms.

How it REALLY works:

• dots in the popup do not correspond to the same points in both eyes-> disparity in the black and white pixels.
• flip the glasses-> make the positive disparity into negative disparity
• Figures out disparity (stereopsis)-> then shape analysis

Question 14

Physiological mechanism of stereopsis

Answer 14

• Binocular cells have receptive fields in each eye
• These come with a range of different separations between the receptive field centers (relative to the fovea of each eye)
• These cells are selective for disparity
• The separation defines the preferred disparity for that cell

Question 15

Binocular Rivalry

Answer 15

• Stereopsis requires matching identical points of the image in the two eyes (e.g., stereogram).
• When the images in the two eyes do not match, the images in the two eyes compete for awareness.
• This alternating perceptual dominance is called binocular rivalry.