l10- depth perception Flashcards
Monocular & Extraretinal Depth Cues
space perception n binocular vision
- retinal image= 2d, world=3d
- visual system must infer depth
Monocular & Extraretinal Depth Cues
problem of depth perception
- how does visual system extract 3d depth in 2d retinal image?
- straight lines=2d curved retina
- euclidean (real-world) input becomes non-euclidean image
- single eye image provides visual angle- small+ near OR big+far
Monocular & Extraretinal Depth Cues
depth cues
- visual signal that indicates 3d structure n distance
Monocular & Extraretinal Depth Cues
monocular depth cues
available w one eye
- pictorial cues: a subset of monocular ones:
- occlusion: blocked objects=farther
- texture gradient: dense texture=farther
- relative height: higher=farther
- relative size:smaller=farther
- familiar size: known object=absolute depthh
- aerial prespective: hazier=farther due to light scattering
- linear prespective: lines converge w distance (vanishing point)
- shading+lighting: interpreted as 3D form assuming light from above
Monocular & Extraretinal Depth Cues
motion based cues
- motion parrallax: as head moves, nearer objects shifts more into the visual fields than further ones
Monocular & Extraretinal Depth Cues
extraretinal depth cues
- accomodation(lens shape change): effective for distance up to 2-3 m
- convergence(eye rotation angle): effective up to 10m, eyes converge (inward) for near objects, diverge (outward) for far ones
Binocular vision & applied stereopsis
Binocular vision
- human field of view: ~190 horizontal, ~110 binocular overlap
- eyes=~6cm apart- each recieves diff image so binocular disparity
Binocular vision & applied stereopsis
binocular disparity
- difference in retinal image=depth cue
Binocular vision & applied stereopsis
stereopsis
- the ability to use disparity as a depth cue
- eg: fixating on red crayon= identical images in both eyes, objects around it=shifted images (disparity increases w distance from fixation)
Binocular vision & applied stereopsis
vieth muller circle
- corresponding retinal points: points equidistant from fovea in both eyes
- VM circle- theortical zone of zero disparity
Binocular vision & applied stereopsis
horopter
- true zero-disparity plane
- flatter than a circle
- deviates systematically from the VM circle
- zero-dispoarity objects lie on the horopter + r seen as fused
- non-zero disparity objects lie off the horopeter n produce diplopia (double vision)
Binocular vision & applied stereopsis
phsyiological diplopia demonstartion
- fixating on a pen:
- distant object=double (NZD)
- pen=fused (zero disparity) - fixated on distant object:
- pen=double
- distant object=fused
Binocular vision & applied stereopsis
panums fusional area
- region where non zero disparities still yield single fused perception
Binocular vision & applied stereopsis
dispairty types
- crossed dispairty: objects closer than fixation
- uncrossed dispairyt: objects farther than fixation
Binocular vision & applied stereopsis
stereocuity
- smallest depth difference detectable~0.1 arc min (0.0016)
- better than visual acuity
- stereoblindness: ~3-5% of ppl cant see disparity
- strabismus(eye misalingment: estropia/exotropia)- loss of stereopsis unless corrected early
Binocular vision & applied stereopsis
neural basis
- binocular neruons in the brain:
- tuned to specific disparities
- also tuned to orientation n spatial frequecny
Binocular vision & applied stereopsis
stereopsis applications n 3d illusions
- stereoscopes (wheatstone, brewtser, holmes)
- random dot stereograms (RDS):
- dots w shifted positions include depth perception
- viewed via stereoscope or free fusion
- anaglyphic RDS: red/cyan images for dichoptic vieiwng
- polarized 3d glasses: modern 3d movies use polarized filters for each eye
Binocular vision & applied stereopsis
stereopsis- real world application
- medical imaging, surgical planning
- robotics, AI, autonomous vehicles
- military, terrain mapping
size constancy
size constancy
- retinal size changes w distance, but percieved size stays constant
- distance is discounted using depth cues- consistent size perception
size constancy
illusions
- ames room: trapezodial room distorts size perception due to misjudged distance
- ponzo illusion: identical lines seem diff sizes due to background depth cues
