3/23/2005 © dr. zachary wartell 1 depth and size perception
Post on 19-Dec-2015
222 views
TRANSCRIPT
3/23/2005 © Dr. Zachary Wartell 1
Depth and Size Perception
3/23/2005 © Dr. Zachary Wartell 2
Human Depth Perception
• Cue Theory – brain learns to identify info. in retinal image that is correlated with depth– oculomotor cues– pictorial cues– movement-produced cues– binocular disparity cues
3/23/2005 © Dr. Zachary Wartell 3
Oculomotor Cues: Accommodation
●susp. lig. kept tight by eye fluid which stretches and thins lens (bend light less)
●cil. mus. (donut shape) contracts allows lens to spring into its natural rounder shape (bend light more)
suspensory ligments
ciliary muscle
3/23/2005 © Dr. Zachary Wartell 4
Oculomotor Cues: Vergence
physical box
eyes
fixation point
3/23/2005 © Dr. Zachary Wartell 5
Oculomotor Cues: Vergence
physical box
eyes
divergence
3/23/2005 © Dr. Zachary Wartell 6
Oculomotor Cues: Vergence
physical box
eyes
convergence
3/23/2005 © Dr. Zachary Wartell 7
Pictorial/Monocular Depth Cues
• overlap/occlusion• size in field of view• height in field of view• atmospheric perspective• familiar size• linear perspective• texture gradiant
3/23/2005 © Dr. Zachary Wartell 8
Overlap/occlusion
• only relative or “ordinal” (psy.) information (partial order - math)
3/23/2005 © Dr. Zachary Wartell 9
Size in field of view
• larger size causes an object to appear closer• Ames balloon experiment
– inflating illuminated balloons in darkened room
3/23/2005 © Dr. Zachary Wartell 10
Height in field of view
3/23/2005 © Dr. Zachary Wartell 11
Atmospheric/aerial Perspective
• farther objects less distinct, color may be less saturated
3/23/2005 © Dr. Zachary Wartell 12
Familiar Size
• knowledge of actual size influences distance judgement
• Epstein (1965)– photo of 3 dime, quarter and nickel at same
size as quarter– viewed by one eye at same distance– darkened room, photo lit by spotlight– judged smaller coin to be closer– binocular viewing foils illusion
3/23/2005 © Dr. Zachary Wartell 13
Linear Perspective
• Leon Battisa Alberti (1435) – principles of perspective drawing
• Leonardo da Vinci – drawing on plane of glass
3/23/2005 © Dr. Zachary Wartell 14
Texture Gradient
• elements that are equally spaced appear closer and closer together in distance
3/23/2005 © Dr. Zachary Wartell 15
ab
Movement-Produced Cue: Motion Parallax
• looking out of car – near objects “move” faster and blur, far objects “move” slower
A B
a'b'
Δa
Δb
ab
3/23/2005 © Dr. Zachary Wartell 16
• related to motion parallax and overlap
Movement-Produced Cue: Deletion & Accretion
Deletion
Accretion
3/23/2005 © Dr. Zachary Wartell 17
Stereopsis
• Wheatstone (1838) – stereoscope showed that differences alone in left/right eye image yields depth
• “stereopsis” – impression of depth due to two different image on retina
3/23/2005 © Dr. Zachary Wartell 18
Corresponding Points
• locations on retina connecting to same part of visual cortex
a'b'
ab
f' f
[Goldstein,44]
3/23/2005 © Dr. Zachary Wartell 19
Corresponding Retinal Points
• locations on retina connecting to same part of visual cortex – roughly equivalent to aligning retina atop one another
a'b'
ab
f' f
left right
3/23/2005 © Dr. Zachary Wartell 20
Horopter
A
B
bl
br
cl
crC
horopteral
bl
cl
cr
ar
br
• A is fixation point• horopter points have
correspondingretinal images
• horopter dependenton fixation pt.
3/23/2005 © Dr. Zachary Wartell 21
Noncorresponding (disparate) retinal points
AB
bl
br
cl
cr
C
horopteral
bl
cl
crar
br
retinal disparity:
θb= θbl-θbr < 0 θc= θcl-θcr > 0
θ<0 θ>0
3/23/2005 © Dr. Zachary Wartell 22
Crossed (<0) versus Uncrossed (>0) disparity
ABC
horopter
uncrossedcrossed
3/23/2005 © Dr. Zachary Wartell 23
Corresponding (Image) Points
• correspondence problem – how does brain determine what left eye image point should be matched with what right eye image point?
(Al Ar)
(Al Cr)
(Cl Cr)
(Ar Cl)
al
cl
crar
?
3/23/2005 © Dr. Zachary Wartell 24
Random-Dot Stereogram - Julesz (1971)
3/23/2005 © Dr. Zachary Wartell 25
Al, Bl
F
FlFr
BA
Br Ar
Rear View
Top ViewHoropter
Zone of SingleVision
Panum’s fusion area
Al, Bl Fl Br Ar
Fr
3/23/2005 © Dr. Zachary Wartell 26
Local vs Global Stereopsis
• local stereopsis – simple stimuli (1 line), small FOV, image correspondence use local info
• global stereopsis – complex stimuli, large FOV, image correspondence needs global info.
• Important: experimental psychophysical results in local & global case can differ
3/23/2005 © Dr. Zachary Wartell 27
Types of stereopsis
• no stereopsis – diplopia / diplopic images, perceived depth at fixation plane or undefined
• patent/quantative stereopsis – magnitude, direction, maybe diplopic, small disparities
• latent/qualitative stereopsis - only direction, always diplopic
3/23/2005 © Dr. Zachary Wartell 28
Human Size Perception
• Visual Angle
3/23/2005 © Dr. Zachary Wartell 29
Law of Size Constancy
• humans correctly perceive an object’s physical size no matter what its distance from us and no matter what the size of image on retina is
• Holway and Boring (1941)
hallways
subject
targetcircle
test circles
1o
3/23/2005 © Dr. Zachary Wartell 30
Holway and Boring (1941)
10 50 100
10
20
30
distance to test circle (ft)
size
of t
arge
t circ
le (
in)
vis. angle
idealall cues
1 eye
+peep hole
+drapes
3/23/2005 © Dr. Zachary Wartell 31
Emmert’s Law
3/23/2005 © Dr. Zachary Wartell 32
References
• E. Bruce Goldstein. Sensation and Perception, 4th Edition. Brooks/Cole Publishing Company, Pacific Grove.