Cognition and Perception

1. Cognition and Perception • This is not a rose. This is not a pipe. “Just try stuffing tobacco in it!” – Rene Magritte, 1930

2. The myth of vision as a faithful record ·       Concentric circles or continuous spiral? ·       The pattern of light is of concentric circles ·       Human vision sees a continuous spiral

3. The Myth of vision as a passive process • The Grand illusion of complete perception • (1) Vision is not rich in detail • the size of a thumbnail at arm’s length is all that gets processed • (2) Attention is limited: the law of ONEs • vision sees one object, one event, one location • These two factors are illustrated by • Impossible triangle • Escher drawings • Bistable images

4. Brains construct a well-behaved 3-D world so we cannot experience a world that is not. Here we see an ordinary triangle and building with normal corners and angles instead of the shocking reality. Why?

9. ·       A perceptually ambiguous wire cube ·       How many different interpretations can you see? Go to: http://mindbluff.com/necker.htm

10. Bi-stable Images

11. Bi-stable Images

12. Figure 1.5. “Subjective” perceptions are not necessarily “arbitrary” perceptions ·       Brains see two instead of all of these interpretations? Why not? ·       Humans bring shared assumptions to the vision project, (1) that objects are generally convex, (2) that straight lines in a picture represent straight edges in an object, and (3) that three-edge junctions are generally right-angled corners.

13. Movement Illusion • http://video.google.com/videoplay?docid=6294268981850523944&ei=r5PRSNGPD6fcqAPS48y6Ag&q=spiral+visual+illusion&vt=lf&hl=en • http://video.google.com/videoplay?docid=-2927422796086500362&vt=lf&hl=en

14. Cognition and Perception • The finished files are the result of years of scientific study combined with the experience of many years. • The finished files are the result of years of scientific study combined with the experience of many years.

15. Gestalt • The whole is greater than the sum of its parts • Law of Pragnanz (“good figure”): We perceive things in the way that is simplest to organize them into cohesive and constant objects.

16. Gestalt Laws Laws of Grouping • 1. Proximity • 2. Similarity • 3. Common fate • 4. Good continuation • 5. Closure/ convexity • 6. Common region • 7. Connectedness • 8. Parse regions at deep concavities

17. Gestalt Laws • Laws of Figure-Ground Segregation • 1. Convex region becomes figure • 2. Smaller region becomes figure • 3. Moving region becomes figure • 4. Symmetric ("good") region becomes figure • 5. Nearer region becomes figure (multiple depth cues apply)

18. Figure 1. A: Kanizsa figure. B: Tse’s volumetric worm. C: Idesawa’s spiky sphere. D: Tse’s sea monster

20. Common Fate • http://dragon.uml.edu/psych/commfate.html

21. Gestalt Laws Laws of Grouping Closure/ convexity

22. Optic Flow • http://www.rdg.ac.uk/ARL/clips/demo_of_displays.htm#opticflow

23. Demos • Charlie Chaplin mask demo • http://www.youtube.com/watch?v=QbKw0_v2clo&feature=related • Visual Illusions • http://www.michaelbach.de/ot/ • Moving random dot stereogram • http://dragon.uml.edu/psych/commfate.html • Spinning silhouette • http://www.youtube.com/watch?v=uBTvKboX84E • Gestalt Illusions • http://www.opprints.co.uk/gallery.php

24. Quizz Which one of the following statements is not true about Gestalt psychology. • It deals with figure-ground segregation • It deals with object recognition • It explains receptive fields • Some of the gestalt principles include: good continuation, common fate and similarity

25. Two Visual SystemsWhat your hands see differs from what the eyes see • Ventral ‘What’ system • Dorsal ‘Where/ How’ system • Brain lesions • Ventral lesions: patients cannot name telephone but mime using it • Dorsal lesions: can name it, but reach in wrong direction for it • Roelofs Effect

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32. Object Recognition

33. Object Recognition(Called Pattern Recognition in Book) • How do you solve problem of Object Constancy? • How does the brain know the objects are the same despite change in perspective?

34. What letter are these, and how do you know? A A A A A A A A A A A A A A A A A A A A

35. Top-Down & Bottom-Up

36. Bottom-Up Processing • Direct Perception theories • Perception comes from the stimuli in the environment • Parts are identified, put together, and then recognition occurs

37. Gibson’s Direct Perception (Ecological model) All the information needed to form a perception is available in the environment Perception is immediate and spontaneous Affordances and attunements Perception and action cannot be separated Action defines the meaningful parameters of perception and provides new ways of perceiving

38. 0 Top-down Processing • Constructive Perception theories • People actively construct perceptions using information based on expectations • Top down processing • Perception is not automatic from raw stimuli • Processing is needed to build perception • Top down processing occurs quickly and involves making inferences, guessing from experience, and basing one perception on another

39. 0 Top-down Processing Evidence • Context effects

40. Theories • Template Matching • Prototype • Feature Matching • Object-Based • Viewer-Based

42. What is relationship between activity in the retina & the brain? • An electrode is inserted into various parts of the visual system (retina, cortex) of an animal. • The cell’s activity in response to the presentation of visual stimuli (lights, bars, complex images) to the animal’s retina is recorded.

44. What is a receptive field of retinal ganglion cells? • The receptive field for these cells is the region of the retina that, when stimulated excites or inhibits the cell’s firing pattern.

46. Are receptive fields of cortical cells like those of retinal ganglion cells? • No!! • Our visual cortex cells respond to more complex stimuli (e.g., bars of light).

47. Hubel & Wiesel (1950s & 60s) • Recorded cortical cells in the visual cortex of cats in response to visual images they presented to the cat’s retina. • They found three types of cells with different receptive fields (bar detectors).

48. Receptive Fields of cortical neurons—Primary Visual cortex • 1. Simple Cells --respond to points of light or bars of light in a particular orientation • 2. Complex cells --respond to bars of light in a particular orientation moving in a specific direction. 3. Hypercomplex Cells: respond to bars of light in a particular orientation, moving in a specific direction, & of a specific line length.

49. Simple Cells

50. Complex Cells