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Perception

Perception. Question of the Day. Why is recognizing an object so easy for humans, but so difficult for computers?. Points of Confusion. http://i.ivillage.com/E/325/Celebrities/FaceReader/FaceReaderIntro_325.jpg. http://www.apogeephoto.com/mag1-6/mag2-5mf1.jpg. Perception:

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Perception

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  1. Perception

  2. Question of the Day • Why is recognizing an object so easy for humans, but so difficult for computers?

  3. Points of Confusion http://i.ivillage.com/E/325/Celebrities/FaceReader/FaceReaderIntro_325.jpg http://www.apogeephoto.com/mag1-6/mag2-5mf1.jpg

  4. Perception: attaching meaning to incoming sensory information What is this?

  5. Bottom-Up Processes The number “4” from the check is compared to a list of stored templates. Template matching

  6. Bottom-Up Processes Problems with Template Matching • Large number of stored templates needed • How are new templates made? • An object can be “more or less” like the template • We can recognize many variations of a template

  7. Bottom-Up Processes Figure 2-8

  8. Bottom-Up Processes Featural Analysis features (“parts”) of a stimulus are recognized by feature detectors and added together to help us perceive an object • Lines or edges • Geons • Phonemes • Parts of a face (eyes, nose…)

  9. Featural Analysis Geons

  10. Figure 2-14 A depiction of Selfridge’s (1959) Pandemonium model. Featural Analysis Letter detection

  11. Bottom-Up Processes Featural Analysis Feature Properties • Detectors can respond at different intensities • Connections between detectors can have different strengths • It is possible to change what a detector will respond to

  12. Bottom-Up Processes Prototype Matching

  13. Bottom-Up Processes Prototype Matching http://www.palm.com

  14. Top-Down Processes Figure 2-19An example of context effects in perception.

  15. Top-Down Processes • Perceptual Learning

  16. Top-Down Processes • Change Blindness http://viscog.beckman.uiuc.edu/grafs/demos/10.html

  17. Top-Down Processes • Word Superiority Effect K K D WORK OWRK

  18. Flying Animal Bottom-Up and Top-Down Processing working together _at Word Perception • Connectionist Model Words Bat Letters B Fox Bat Fat Features (lines) I Rat Cat

  19. Theories of Perception • Gestalt Psychology (Wertheimer, Koffka, and Kohler – 1920s) • “The whole differs from the sum of its parts” • Perception is not built up from sensations but is a result of perceptual organization • We use heuristics to make “best guesses” about the identity of stimuli

  20. The Gestalt Approach • Principles of perceptual organization • Pragnanz - every stimulus is seen as simply as possible

  21. Figure 2-5 Gestalt principles of Perceptual Organization

  22. Gestalt principles of Perceptual Organization • Similarity • http://www.aber.ac.uk

  23. not this what most people would see Gestalt principles of Perceptual Organization • Good continuation • http://www.aber.ac.uk

  24. The Gestalt Approach • Principles of perceptual organization • Good continuation • Connected points resulting in straight or smooth curves belong together • Lines are seen as following the smoothest path http://www.owlnet.rice.edu/~psyc351/Images/Wolfe-Fig-04-07-0.jpg http://graphicdesign.spokanefalls.edu/tutorials/process/gestaltprinciples/continuation/continuation_a.gif

  25. Gestalt principles of Perceptual Organization • http://www.aber.ac.uk • Proximity

  26. The Gestalt Approach • Principles of perceptual organization • Proximity - things that are near to each other are grouped together

  27. Gestalt principles of Perceptual Organization • Common fate http://www.tutkie.tut.ac.jp/~mich/humanmotion.gif

  28. The Gestalt Approach • Principles of perceptual organization • Meaningfulness or familiarity - things form groups if they appear familiar or meaningful http://www.customflamepainting.com/noncgi_parts/upload/samples.901.11.jpg

  29. The Gestalt Approach • Principles of perceptual organization • Common region - elements in the same region tend to be grouped together • Uniform connectedness - connected region of visual properties are perceived as single unit • Synchrony - elements occurring at the same time are seen as belonging together

  30. Perceptual Segregation • Properties of figure and ground • The figure is more “thinglike” and more memorable than ground • The figure is seen in front of the ground • The ground is more uniform and extends behind figure • The contour separating figure from ground belongs to the figure

  31. Perceptual Segregation • Figure-ground segregation - determining what part of environment is the figure so that it “stands out” from the background • Reversible figure-ground

  32. Perceptual Segregation http://www.apogeephoto.com/mag1-6/mag2-5mf1.jpg

  33. Gestalt principles of Perceptual Organization • Closure http://daphne.palomar.edu

  34. Figure 3-26 (p. 91)Example of stimuli used in the PET scan study of processing words. Word Perception • Neuropsychological Perspective

  35. Direct Perception vs. Constructivist Approach • Biological motion • http://www.psico.univ.trieste.it/labs/acn-lab/eng_p/e051c1m1_curr.html

  36. Optic flow

  37. Direct Perception • Affordances: • Information from the stimulus that specifies how it can be used

  38. Visual Agnosia http://scien.stanford.edu/class/psych221/projects/06/cukur/intro_files/image021.jpg

  39. Visual Agnosia • Associative Visual Agnosia • Can copy, but unaware what it is; cannot assign meaning to object • Difficulty in transferring visual info into words • Apperceptive Visual Agnosia • Cannot recognize by shape • Cannot copy drawings • Often involves ‘prosopagnosia’ http://scien.stanford.edu/class/psych221/projects/06/cukur/intro_files/image021.jpg

  40. Agnosia

  41. Identification of Faces and Members of CategoriesProsopagnosia The Fusiform Face Area: http://www.psy.vanderbilt.edu/faculty/gauthier/picts/mona_lisa.jpg

  42. Perceptual Intelligencelight-from-above heuristic

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