Topic 5: Depth and Size

Question 1

how do we perceive depth?

Answer 1

distal stim is 3d object in space
proximal stim is 2d image on retina
all distance/size leads to same size on retina

Question 2

convergence

accomodation

Answer 2

inward movement of eyes when we focus on nearby objects, parallel when far away
-shape of lens when we focus on objects at different distances (flat when object is close - bends light)

Question 3

Relative depth

actual depth

Answer 3

depth of objects compared to one another

-distance of object from observer

Question 4

occlusion

relative height

Answer 4

• when object partially covers another, we think object blocking is closer at any distance
• objects closer to the horizon line appear more distant

Question 5

familiar size

relative size

Answer 5

distance info is based on our knowledge of object size

-for objects of equal size closer one takes up more of visual field

Question 6

perspective convergence

atmospheric perspective

Answer 6

parallel lines appear to come together in the distance

-distant objects are fuzzier and have a blue tint

Question 7

texture gradient

Answer 7

equally spaced elements seem more closely packed as distance increases - cranberry example
-lower frequency in foreground

Question 8

shadows

Answer 8

indicate where objects are located

where shadow is can change perception of depth even if they are actually at the same depth

Question 9

motion parallax

Answer 9

close objects glide past rapidly but distant objects appear to move slowly
on orthogonal plane
you dont have to be moving

Question 10

deletion and accretion

Answer 10

objects are covered (deletion) or uncovered (accretion) as we move relative to them or they move relative to us

Question 11

stereoscopic depth perception

binocular disparity

Answer 11

depth perception created by both eyes, phenomology is very different from monocular depth perception
-difference in images on L and R retinas, different POV for the 2 eyes

Question 12

corresponding and noncorresponding retinal points

Answer 12

object ON horopter fall on corresponding points

-objects OFF horopter fall on noncorresponding points

Question 13

uncrossed disparity

crossed disparity

Answer 13

causes images on both retinas to move nasally relative to location of images on objects on horopter
-objects closer on horopter will move temporally on both retinas compared to objects on horopter

Question 14

absolute disparity

relative disparity

Answer 14

• angle from corresponding point, determines from horopter and changes with gaze
• differences in disparities between objects, determines distance between objects and unchanged with gaze

Question 15

stereopsis

correspondence problem

Answer 15

perception of depth due to binocular disparity

• random dot stereogram, autostereogram, animated autosterogram
• how to match 2 points on retinal images - use features of objects

Question 16

relationship of depth and size

Answer 16

-a small near object and large distant object can have identical visual angles and retinal images
size constancy

Question 17

size-distance scaling

Answer 17

S=K(RxD)
s=perceived distance
D= perceived distance
R= size of retinal image
K= constant

Question 18

ponzo illusion

ames room

Answer 18

same size on page but different perceived size due to different perceived depth

• retinal image (R) is the same but perceived distance (D) is different
• brain assumes walls will be the same size and overrides changing size of people - assumption of parallel walls

Question 19

dorsal and ventral stream

Answer 19

absolute disparity and guiding action

-relative disparity and ID obects

Question 20

anagylph

polarized

Answer 20

• uses coloured lenses to deliver one image to each eye

- deliver image to one eye in orthogonal direction, one is horizontal and other is vertical

Question 21

active shutter
interference filter technology
parallax barrier technology

Answer 21

uses LCD lenses to open/close in turn
-using different wavelengths to create independent images (IMAX)
use tiny barriers to allow one image per eye (Nintendo 3ds)