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Visual Perception

Visual Perception . Cecilia R. Aragon IEOR 170 UC Berkeley Spring 2006. Acknowledgments. Thanks to slides and publications by Pat Hanrahan, Christopher Healey, Maneesh Agrawala, and Lawrence Anderson-Huang. Visual perception. Structure of the Retina Preattentive Processing Detection

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Visual Perception

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  1. Visual Perception Cecilia R. Aragon IEOR 170 UC Berkeley Spring 2006

  2. Acknowledgments • Thanks to slides and publications by Pat Hanrahan, Christopher Healey, Maneesh Agrawala, and Lawrence Anderson-Huang. IEOR 170

  3. Visual perception • Structure of the Retina • Preattentive Processing • Detection • Estimating Magnitude • Change Blindness • Multiple Attributes • Gestalt IEOR 170

  4. Visual perception and psychophysics Psychophysics is concerned with establishing quantitative relations between physical stimulation and perceptual events. IEOR 170

  5. Structure of the Retina IEOR 170

  6. Structure of the Retina • The retina is not a camera! • Network of photo-receptorcells (rods and cones) andtheir connections [Anderson-Huang, L. http://www.physics.utoledo.edu/~lsa/_color/18_retina.htm] IEOR 170

  7. Photo-transduction • When a photon enters a receptor cell (e.g. a rod or cone), it is absorbed by a molecule called 11-cis-retinal and convertedto trans form. • The different shapecauses it to ultimatelyreduce the electricalconductivity of thephoto-receptor cell. [Anderson-Huang, L. http://www.physics.utoledo.edu/~lsa/_color/18_retina.htm] IEOR 170

  8. Electric currents from photo-receptors • Photo-receptors generate an electrical current in the dark. • Light shuts off the current. • Each doubling of light causes roughly the same reduction of current (3 picoAmps for cones, 6 for rods). • Rods more sensitive, recover more slowly. • Cones recover faster, overshoot. • Geometrical response in scaling laws of perception. [Anderson-Huang, L. http://www.physics.utoledo.edu/~lsa/_color/18_retina.htm] IEOR 170

  9. Preattentive Processing

  10. How many 5’s? 385720939823728196837293827 382912358383492730122894839 909020102032893759273091428 938309762965817431869241024 [Slide adapted from Joanna McGrenere http://www.cs.ubc.ca/~joanna/ ] IEOR 170

  11. How many 5’s? 385720939823728196837293827 382912358383492730122894839 909020102032893759273091428 938309762965817431869241024 IEOR 170

  12. Preattentive Processing • Certain basic visual properties are detected immediately by low-level visual system • “Pop-out” vs. serial search • Tasks that can be performed in less than 200 to 250 milliseconds on a complex display • Eye movements take at least 200 msec to initiate IEOR 170

  13. Color (hue) is preattentive • Detection of red circle in group of blue circles is preattentive [image from Healey 2005] IEOR 170

  14. Form (curvature) is preattentive • Curved form “pops out” of display [image from Healey 2005] IEOR 170

  15. Conjunction of attributes • Conjunction target generally cannot be detected preattentively (red circle in sea of red square and blue circle distractors) [image from Healey 2005] IEOR 170

  16. Healey appleton preattentive processing http://www.csc.ncsu.edu/faculty/healey/PP/index.html IEOR 170

  17. line orientation length width size curvature number terminators intersection Preattentive Visual Features closure color (hue) intensity flicker direction of motion stereoscopic depth 3D depth cues IEOR 170

  18. Cockpit dials • Detection of a slanted line in a sea of vertical lines is preattentive IEOR 170

  19. Detection IEOR 170

  20. Just-Noticeable Difference • Which is brighter? IEOR 170

  21. Just-Noticeable Difference • Which is brighter? (130, 130, 130) (140, 140, 140) IEOR 170

  22. Weber’s Law • In the 1830’s, Weber made measurements of the just-noticeable differences (JNDs) in the perception of weight and other sensations. • He found that for a range of stimuli, the ratio of the JND ΔS to the initial stimulus S was relatively constant: ΔS / S = k IEOR 170

  23. Weber’s Law • Ratios more important than magnitude in stimulus detection • For example: we detect the presence of a change from 100 cm to 101 cm with the same probability as we detect the presence of a change from 1 to 1.01 cm, even though the discrepancy is 1 cm in the first case and only .01 cm in the second. IEOR 170

  24. Weber’s Law • Most continuous variations in magnitude are perceived as discrete steps • Examples: contour maps, font sizes IEOR 170

  25. Estimating Magnitude IEOR 170

  26. Stevens’ Power Law • Compare area of circles: IEOR 170

  27. Stevens’ Power Law s(x) = axb s is the sensation x is the intensity of the attribute a is a multiplicative constant b is the power b > 1: overestimate b < 1: underestimate [graph from Wilkinson 99] IEOR 170

  28. [Stevens 1961] Stevens’ Power Law IEOR 170

  29. Stevens’ Power Law Experimental results for b: Length .9 to 1.1 Area .6 to .9 Volume .5 to .8 Heuristic: b ~ 1/sqrt(dimensionality) IEOR 170

  30. Stevens’ Power Law • Apparent magnitude scaling [Cartography: Thematic Map Design, p. 170, Dent, 96] S = 0.98A0.87 [J. J. Flannery, The relative effectiveness of some graduated point symbols in the presentation of quantitative data, Canadian Geographer, 8(2), pp. 96-109, 1971] [slide from Pat Hanrahan] IEOR 170

  31. Most accurate Least accurate Position (common) scale Position (non-aligned) scale Length Slope Angle Area Volume Color (hue/saturation/value) Relative Magnitude Estimation IEOR 170

  32. Change Blindness IEOR 170

  33. Change Blindness • An interruption in what is being seen causes us to miss significant changes that occur in the scene during the interruption. • Demo from Ron Rensink: http://www.psych.ubc.ca/~rensink/flicker/ IEOR 170

  34. Possible Causes of Change Blindness [Simons, D. J. (2000), Current approaches to change blindness, Visual Cognition, 7, 1-16. ] IEOR 170

  35. Multiple Visual Attributes IEOR 170

  36. The Game of Set • Color • Symbol • Number • Shading A set is 3 cards such that each feature is EITHER the same on each card OR is different on each card. [Set applet by Adrien Treuille, http://www.cs.washington.edu/homes/treuille/resc/set/] IEOR 170

  37. Multiple Visual Attributes • Integral vs. separable • Integral dimensions • two or more attributes of an object are perceived holistically (e.g.width and height of rectangle). • Separable dimensions • judged separately, or through analytic processing (e.g. diameter and color of ball). • Separable dimensions are orthogonal. • For example, position is highly separable from color. In contrast, red and green hue perceptions tend to interfere with each other. IEOR 170

  38. Integral vs. Separable Dimensions Integral Separable [Ware 2000] IEOR 170

  39. Gestalt IEOR 170

  40. Gestalt Principles • figure/ground • proximity • similarity • symmetry • connectedness • continuity • closure • common fate • transparency IEOR 170

  41. Examples Figure/Ground Proximity Connectedness [from Ware 2004] [http://www.aber.ac.uk/media/Modules/MC10220/visper07.html] IEOR 170

  42. Conclusion • What is currently known about visual perception can aid the design process. • Understanding low-level mechanisms of the visual processing system and using that knowledge can result in improved displays. IEOR 170

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