3/23/2005 © Dr. Zachary Wartell 1 Depth and Size Perception.

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Presentation 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 a b Movement-Produced Cue: Motion Parallax looking out of car – near objects “move” faster and blur, far objects “move” slower A B a'a' b'b' ΔaΔa ΔbΔb a b

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'a' b'b' a b f'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'a' b'b' a b f'f' f leftright

3/23/2005 © Dr. Zachary Wartell 20 Horopter A B  bl  br  cl  cr C horopter alal blbl clcl crcr arar brbr A is fixation point horopter points have corresponding retinal images horopter dependent on fixation pt.

3/23/2005 © Dr. Zachary Wartell 21 Noncorresponding (disparate) retinal points A B  bl  br  cl  cr C horopter alal blbl clcl crcr arar brbr retinal disparity: θ b = θ bl -θ br < 0 θ c = θ cl -θ cr > 0 θ<0 θ>0

3/23/2005 © Dr. Zachary Wartell 22 Crossed ( 0) disparity A B C horopter uncrossed crossed

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? (A l A r ) (A l C r ) (C l C r ) (A r C l ) alal clcl crcr arar ?

3/23/2005 © Dr. Zachary Wartell 24 Random-Dot Stereogram - Julesz (1971)

3/23/2005 © Dr. Zachary Wartell 25 A l, B l F FlFl FrFr B A BrBr ArAr Rear View Top View Horopter Zone of Single Vision Panum’s fusion area A l, B l FlFl BrBr ArAr FrFr

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 target circle test circles 1o1o

3/23/2005 © Dr. Zachary Wartell 30 Holway and Boring (1941) distance to test circle (ft) size of target circle (in) vis. angle ideal all 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, 4 th Edition. Brooks/Cole Publishing Company, Pacific Grove.