Depth Perception Important Terms

Question 1

Accomodation

Answer 1

Crystalline lens gets fatter to focus on nearby objects; gets thinner to focus on farwaway objects

ciliary mucles provide feedback info on lens curvature and therefor distance

Question 2

Convergence

Answer 2

rotation of eyes inward to cause image to fall on the fovea

large converge angle = closer object, smaller convergence angle = farther object

Question 3

Binocular/ Retinal Disparity

Answer 3

Retinal images of an object fall on disparate points on each eye’s retina, fixated object produces no disparity

Question 4

Horopter

Answer 4

imaginary surface passing through fixation point; retinal images of objects not on horopter create disparate points on each eye’s retina

farther from horopter = greater disparity

Question 5

Degree of disparity

Answer 5

distance between points on each retina

greater disparity = further from horopter

Question 6

Panum’s Fusional Area (PFA)

Answer 6

spatial points that fall on noncorresponding retinal areas, but lie within the PFA are fused into single images

eg. Hubel and Wiesel found cells in the visual cortex that responded most to certain differences in degrees of disparity (objects not on horopter)

Question 7

Stereopsis

Answer 7

perception of depth based on retinal disparity alone

eg. random dot stereograms which eliminate monocluar depth cues - each eye sees path oc random dots with no apparant global shape, in each path is a square shaped region that is shifted over in each eye. This creates retinal disparity; shifted pattern is perceived as a floating 3D region

shows stereopsis is not dependent on detection of form occuring first

Question 8

Feature-Based Methods

Answer 8

solves correspondence problem based on making a match based on extracted image structure

Question 9

Correlation-Based Methods

Answer 9

based on grey-level descriptions,

look for statistically likely to match

Question 10

Spring-Coupled Magnetic Dipole Model

Answer 10

makes global match, to induce fusion both images must lie on horopter, only neurons responding to 0 degrees disparity are involved, after images have fused, you can move them off the horopter without losing fusion within the pFA (hsyteresis effect)

Question 11

Compatibility

Answer 11

Is a natural constraint exploited by Marrs program
to be matched, points on retina must be physically similair

eg. dark features in one correspond to dark features in the other

Question 12

Uniqueness

Answer 12

a feature on one retina should correspond uniquely to one feature on the other retina,

violated in the case of transparent surfaces when an image feature is a combination of points from two physical surfaces

Question 13

Continuity

Answer 13

disparity should vary smoothly

if two matched features are close together in the images their disparities should be similair - due to how the environment is made of continuous surfaces separated by boundaries

changes in disparity should be rare, occuring only at surface boundaries

Question 14

Successive Illusions

Answer 14

require adapting phase, most visual illusions are simultaneous

effect caused by interacting stimuli

eg. aftereffects

Question 15

size-distance scaling

Answer 15

distance is taken into account when perceive size (size constancy), as distance from given object increases retinal image becomes smaller yet we do not perceive object as getting smaller

eg. Ponzo illusion: converging lines are a depth cue that activates size constancy: 2D image treated like 3D due to size-distance scaling upper bar seems farther away and thus larger