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Depth and Size Perception

Depth and Size Perception. 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. Oculomotor Cues: Accommodation.

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Depth and Size Perception

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  1. Depth and Size Perception © 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 © 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) ciliary muscle suspensory ligments © Dr. Zachary Wartell

  4. Oculomotor Cues: Vergence eyes fixation point physical box © Dr. Zachary Wartell

  5. Oculomotor Cues: Vergence eyes divergence physical box © Dr. Zachary Wartell

  6. Oculomotor Cues: Vergence eyes convergence physical box © 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 © Dr. Zachary Wartell

  8. Overlap/occlusion • only relative or “ordinal” (psy.) information (partial order - math) © 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 © Dr. Zachary Wartell

  10. Height in field of view © Dr. Zachary Wartell

  11. Atmospheric/aerial Perspective • farther objects less distinct, color may be less saturated © 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 © Dr. Zachary Wartell

  13. Linear Perspective • Leon Battisa Alberti (1435) – principles of perspective drawing • Leonardo da Vinci – drawing on plane of glass © Dr. Zachary Wartell

  14. Texture Gradient • elements that are equally spaced appear closer and closer together in distance © Dr. Zachary Wartell

  15. Movement-Produced Cue: Motion Parallax a a b b Δa Δb b' a' • looking out of car – near objects “move” faster and blur, far objects “move” slower A B © Dr. Zachary Wartell

  16. Movement-Produced Cue: Deletion & Accretion • related to motion parallax and overlap Deletion Accretion © 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 © Dr. Zachary Wartell

  18. Corresponding Points • locations on retina connecting to same part of visual cortex a a' b b' f f' [Goldstein,44] © 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' f f' left right © Dr. Zachary Wartell

  20. Horopter cl • A is fixation point • horopter points havecorrespondingretinal images • horopter dependenton fixation pt. horopter al bl cl B bl A cr C cr ar br br © Dr. Zachary Wartell

  21. Noncorresponding (disparate) retinal points bl horopter al bl cl cl θ<0 θ>0 C A B retinal disparity: θb= θbl-θbr < 0 θc= θcl-θcr > 0 cr cr ar br br © Dr. Zachary Wartell

  22. Crossed (<0) versus Uncrossed (>0) disparity horopter uncrossed crossed C A B © 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 cl ? (Ar Cl) (Cl Cr) (Al Ar) (Al Cr) cr ar © Dr. Zachary Wartell

  24. Random-Dot Stereogram - Julesz (1971) © Dr. Zachary Wartell

  25. Panum’s fusion area TopView Horopter B A F Zone of Single Vision Al, Bl Fr Br Ar Fl Rear View Fr Al, Bl Br Fl Ar © 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 © 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 © Dr. Zachary Wartell

  28. Human Size Perception • Visual Angle © 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) target circle hallways subject 1o test circles © Dr. Zachary Wartell

  30. Holway and Boring (1941) all cues ideal 30 1 eye 20 size of target circle (in) +peep hole 10 +drapes vis. angle 50 100 10 distance to test circle (ft) © Dr. Zachary Wartell

  31. Emmert’s Law © Dr. Zachary Wartell

  32. References • E. Bruce Goldstein. Sensation and Perception, 4th Edition. Brooks/Cole Publishing Company, Pacific Grove. © Dr. Zachary Wartell

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