how do we perceive depth?
distal stim is 3d object in space
proximal stim is 2d image on retina
all distance/size leads to same size on retina
convergence
accomodation
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)
Relative depth
actual depth
depth of objects compared to one another
-distance of object from observer
occlusion
relative height
- when object partially covers another, we think object blocking is closer at any distance
- objects closer to the horizon line appear more distant
familiar size
relative size
distance info is based on our knowledge of object size
-for objects of equal size closer one takes up more of visual field
perspective convergence
atmospheric perspective
parallel lines appear to come together in the distance
-distant objects are fuzzier and have a blue tint
texture gradient
equally spaced elements seem more closely packed as distance increases - cranberry example
-lower frequency in foreground
shadows
indicate where objects are located
where shadow is can change perception of depth even if they are actually at the same depth
motion parallax
close objects glide past rapidly but distant objects appear to move slowly
on orthogonal plane
you dont have to be moving
deletion and accretion
objects are covered (deletion) or uncovered (accretion) as we move relative to them or they move relative to us
stereoscopic depth perception
binocular disparity
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
corresponding and noncorresponding retinal points
object ON horopter fall on corresponding points
-objects OFF horopter fall on noncorresponding points
uncrossed disparity
crossed disparity
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
absolute disparity
relative disparity
- angle from corresponding point, determines from horopter and changes with gaze
- differences in disparities between objects, determines distance between objects and unchanged with gaze
stereopsis
correspondence problem
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
relationship of depth and size
-a small near object and large distant object can have identical visual angles and retinal images
size constancy
size-distance scaling
S=K(RxD) s=perceived distance D= perceived distance R= size of retinal image K= constant
ponzo illusion
ames room
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
dorsal and ventral stream
absolute disparity and guiding action
-relative disparity and ID obects
anagylph
polarized
- 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
active shutter
interference filter technology
parallax barrier technology
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)
