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2. Chapter 2 Perception cogch22

3. 3 Extramission: Extramission: seeing occurs by something issuing from the eye Study found that 69% of college students held this misunderstanding. (Winer, Cottrell, Gref, Fournier & Bica, 2002)

4. cogch24 Assume a real world exists out there!!! Distal Stimuli How do we get information about it into our cognitive systems?

5. cogch2 5 The response of sensory receptors is referred to as the Proximal Stimuli. Percept is information that is processed for meaning. Perception involves reducing and categorizing information.

6. cogch26 Vision - Light Waves Hearing - Sound Waves Taste & Smell - Chemicals Touch & Pain - Direct Pressure Information about Distal Stimuli is carried by Energy

7. cogch27 Visual Perception Qualities of Light that make it ideal for carrying information fast constant speed travels in straight lines abundant Predictably interacts with object surfaces - absorbed (by pigments) - reflected

8. cogch28 Retina has three layers of neurons 1)is a single layer of photo sensitive cells (rods & cones) 2) Bipolar cells 3) Ganglion cells

9. cogch29 Photoreceptors – Rods and Cones Transduce light into neural messages.

10. cogch210 Cone system has 3 types of Cone shaped photoreceptors Each with a different type of Photopigment. The Rod system has 1 type of Rod shaped Photoreceptor with a photopigment called rhodopsin. Rod vision responds to the full range of light wavelenghts.

11. cogch211 Visual Information is carried by the optic nerve which crosses hemispheres at the optic chiasm. The optic tract then carries the neural messages to the visual receiving area in the occipital lobe.

12. cogch212 Information from both eyes is carried to each the occipital lobe of both hemispheres of the brain.

13. cogch213 130 million photoreceptors per eye. 1 million ganglion neurons leave each eye. Conclusion: A lot of processing of visual information goes on in the nerve cells of the eye. Compression.

14. cogch214 Photoreceptors pass info to collector cells which pass it on to ganglion cells.

15. cogch215 Compression occurs through synapses made between receptors and connector cells (horizontal cells, Bipolar cells and amacrine cells) and ganglion cells

16. cogch216 Compression - reduction in neural messages Between photoreceptors and Ganglion cells. RodsCones 120 million 7 million Ganglion 1 Million

17. cogch217 Approx 120 rods compress onto a single ganglion. Approx 6 cones compress onto a single ganglion. Effects of Convergence. When a large number of photoreceptors are converged on a single Ganglion cell, acuity (detail) is lost, but sensitivity is gained.

18. cogch218 Why do Cones have greater acuity? Less convergence. Maintains specific location.

19. cogch219 Fovea mostly cones densely packed provides most accurate precise vision

20. cogch220 A great deal of processing is done before the visual information leaves the eye.

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22. cogch222 Mach Bands - Edge Enhancement Illusion Between two regions of different intensity a thin bright band appears at the lighter side and a thin dark band appears on the darker side.

23. cogch223 Hermann Grid When the viewer looks at the grid, the white dots and the center of each 'corridor' seem to shift between white and gray. When the viewer focused his or her attention on a specific dot, it is obvious that it is white. But as soon as attention is shifted away, the dot shifts to a gray color.

24. cogch224 Processes (neural cross-talk) that occurs in the eye, detects and emphasize important aspects of the visual stimuli, while removing redundant information.

25. cogch225 Sensation vs. Perception Sensation is the registration of sensory input at the sensory receptor cells (proximal). Perception is the process of interpreting and understanding sensory information (precept).

26. cogch226 Saccades- Saccades- Eye movements from point to point. Fixations Fixations- pauses in eye movement. During the saccade there is suppression of the normal visual processes. Visual Information is taken in only during fixations.

27. cogch227 Your visual system is really just sampling the scene. Your sensory processors are selective – maintaining attention to stimuli that are important – while tuning out those that are not.

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29. cogch229 By looking at the grid you can see that your brain is continuously trying to figure out if there's anything meaningful hidden in the pattern. perceptual organization First it tries one approach, then another, then another until it finds something it can recognize. Called perceptual organization.

30. cogch230 Gestalt Approach Gestalt is a psychology term which means "unified whole". It refers to theories of visual perception developed by German psychologists in the 1920s. These theories attempt to describe how people tend to organize visual elements into groups or unified wholes when certain principles are applied.

31. cogch231 The Whole is different than the sum of its parts.

32. cogch232 Figure-Ground Tendency to separate a visual display into figure and ground. One part is depicted as Figure and the other as Ground.

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35. cogch235 Gestalt Principles of Perceptual Organization Law of Pragnanz (good form or simplicity)

36. cogch236 Objects with similar properties (e.g. shape, color) Nearby objects Objects that define smooth lines or curves Objects that form symmetrical patterns Objects that form periodic patterns

37. cogch237 The example above (containing 11 distinct objects) appears as single unit because all of the shapes have similarity. Similarity occurs when objects look similar to one another. People often perceive them as a group or pattern.

38. cogch238 Good Continuation: Group together items that follow in a straight or smooth line. Common Fate

39. cogch239 Closure Closure occurs when an object is incomplete or a space is not completely enclosed. If enough of the shape is indicated, people perceive the whole by filling in the missing information. Although the panda above is not complete, enough is present for the eye to complete the shape. When the viewer's perception completes a shape, closure occurs.

40. cogch240 Witness the Ontario launch of the "Flick Off" campaign, and Environment Minister Laurel Broten's desperate attempt to maintain her dignity in front of its official logo. Campaign is aimed at getting young people to cut energy use http://www.cbc.ca/canada/toronto/story/2007/04/26/flick-off- campaign.html#ixzz0fnapnrAP http://www.cbc.ca/canada/toronto/story/2007/04/26/flick-off- campaign.html#ixzz0fnapnrAP

41. cogch241 Bottom-Up Processing In the bottom-up processing approach, perception starts at the sensory input of the stimulus. Thus, perception can be described as data-driven. For example, there is a flower at the center of a person's field. The sight of the flower and all the information about the stimulus are carried from the retina to the visual cortex in the brain. The signal travels in one direction.

42. cogch242 Examples of Bottom-Up Approaches Template Theories Comparing the 2-D shape of the object with stored shapes in Memory (template). Problems 1)Too many templates would be needed. 2) Inflexible

43. cogch243 Same object at different viewing angles has very different shapes. Rotational Invariance: People are capable of recognizing objects from many different vantage points, even views that have never before been seen (Biederman & Gerhardstein, 1993).

44. cogch244 Many things we can readily distinguish have very similar shapes.

45. cogch245 Feature Analysis or Detection: break objects down into features and match against stored object features.

46. cogch246 Do Feature Recognition Models Make Sense?? Evidence: Neurological: feature detectors in visual cortex Hubel & Wiesel (1965). - located feature neurons that respond best to specific feature “line orientations, curves, corners ends”.

47. cogch247 Video

48. cogch248 Feature detectors are neurons that respond to specific features of the environment, such as lines, orientation, edges (end-stops), and movement.

49. cogch249 Where are the feature detectors? Retina or Visual Cortex of Brain? Motion Illusion If people CANNOT see the "wave/spiral/afterimage" effect using the eye that was shut, then the feature detectors must be in our retina. If people generally still have the "wave/spiral/afterimage" effect using the eye that was shut, then the feature detectors are in the visual cortex.

50. cogch250 Most Feature theories assume that perception involves processing of features followed by more global or general processing to integrate information from features. Evidence shows however that GLOBAL processing can precede processing of features.

51. cogch251 Navon (1977) Participants shown series of stimuli in which a larger letter was made up of small letters.

52. cogch252 On some trials they were asked to identify whether the large letter (Global) was an H or an S. On other trials whether the small (feature) letters were an H or an S. When identifying the small letters they were much slower when the features were inconsistent with the Global Letter. Slower than

53. cogch253 Indicates that processing of the Global meaning interferes with the identification of the features. But Identifying the Larger Letter was not effected by what type of feature letter it was made up by. Indicates that we may identify global objects or scenes before we process features!!

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56. Object Superiority Effect Weisstein & Harris (1974) Line drawings are seen as box-like three-dimensional figures if the lines are arranged properly. A flat two- dimensional pattern is seen when these same lines are disarranged. A target line contained within the three- dimensional figure (A) is identified more readily than is the same line contained within a two-dimensional figure (B). cogch256

57. What is this word? cogch257

58. cogch258 Limitations of Feature Analysis Models Bottom-up models do not account for the large effects of context (i.e., surrounding information, your knowledge and expectations). Proof Reading Effects Repetition Blindness

59. Top-Down Processes Conceptually-driven processes provide expectations from the top-down and speed processing of features. cogch259

60. cogch260 Word Superiority Effect (Reicher, 1969) Letter strings flashed very briefly ONFK WORK K A target letter K is shown Task: Respond “Y” if target was present

61. Word Superiority Effect WORK vs. ORWK vs. K Surprisingly, a single letter (K) is recognized faster in the context of a whole word (WORK) than when presented as an isolated letter. A nonword (ORWK) doesn’t provide this top-down advantage. cogch261

62. cogch262 Parallel Distributed Processing Parallel - Features, Letters, words, all processed at the same time. Distributed - Processing at several levels

63. Fingerprints, Experts and Emotions “At present many agencies give fingerprint experts contextual information about the crime, which may, clearly, bias their decisions in marginal cases. One simple recommendation would be to just provide experts with the fingerprints and no other contextual information.” cogch263

64. Implicit and Analytic Reasoning Experts often begin by useing more implicit reasoning (fast/top-down) and cross-check using more analytic processes. Novices rely more on analytic reasoning. cogch264

65. Visual Object Recognition cogch265

66. Recognition-By-Components Theory Biederman (1987) –Describes how 3D images are identified –Breaks objects down into geons –Objects are identified by geons and relationship between them cogch266

67. cogch267 View Invariant: Look the same from most angles Spatial arrangement of geons is the same. Biederman & Gerhardstein (1993) Priming Study

68. cogch268 Discriminable Difficult to confuse one for another Noise Resistant Can be identified under less-than- ideal conditions

69. cogch269 True only if non-relational information is intact. Take away information about how the Geons go together (vertexes) recognition takes longer. Blotted Letters

70. cogch270 Parsimonious 36 Geons can define 150 million 3-geon objects. Allows novel stimuli to be identified by comparing Geon structures to similar stored stimuli.

71. cogch271 Is object recognition really view independent?? It depends! When making easy discriminations it is (comparing a Dog to a Car). When the task requires difficult within category discriminations (distinguishing on type of car from another?)

72. cogch272 Foster & Gilson (2002) Are the two objects the same? Differ on viewpoint-invariant feature (number of parts) or viewpoint-variant features (part length). Participants showed evidence of using viewpoint- invariant and viewpoint variant processing depending on the demands of the task.

73. cogch273 Top Down Influences Allow us to Get meaning out of even minimal Perceptual information. Biological Motion

74. cogch274 Perception improves with practice as long as practice has feedback! Practice increases Top-down factors.