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2. Chapter 2 Perception cogch2

3. 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) cogch2

4. Assume a real world exists out there!!! Distal Stimuli How do we get information about it into our cognitive systems? 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. cogch2

6. Information about Distal Stimuli is carried by Energy • Vision - Light Waves • Hearing - Sound Waves • Taste & Smell - Chemicals • Touch & Pain - Direct Pressure cogch2

7. 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 cogch2

8. Retina has three layers of neurons • is a single layer of photo sensitive cells (rods & cones) 2) Bipolar cells 3) Ganglion cells cogch2

9. Photoreceptors – Rods and Cones Transduce light into neural messages. cogch2

10. 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. cogch2

11. 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. cogch2

12. Information from both eyes is carried to each the occipital lobe of both hemispheres of the brain. cogch2

13. 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. cogch2

14. Photoreceptors pass info to collector cells which pass it on to ganglion cells. cogch2

15. Compression occurs through synapses made between receptors and connector cells (horizontal cells, Bipolar cells and amacrine cells) and ganglion cells cogch2

16. Compression - reduction in neural messages Between photoreceptors and Ganglion cells. Rods Cones 120 million 7 million Ganglion 1 Million cogch2

17. 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. cogch2

18. Why do Cones have greater acuity? Less convergence. Maintains specific location. cogch2

19. Fovea • mostly cones • densely packed • provides most accurate precise vision cogch2

20. A great deal of processing is done before the visual information leaves the eye. cogch2

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22. 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. cogch2

23. 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. cogch2

24. Processes (neural cross-talk) that occurs in the eye, detects and emphasize important aspects of the visual stimuli, while removing redundant information. cogch2

25. 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). cogch2

26. Saccades- Eye movements from point to point. Fixations- pauses in eye movement. During the saccade there is suppression of the normal visual processes. Visual Information is taken in only during fixations. cogch2

27. 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. cogch2

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29. 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. First it tries one approach, then another, then another until it finds something it can recognize. Called perceptual organization. cogch2

30. 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. cogch2

31. The Whole is different than the sum of its parts. cogch2

32. Figure-Ground Tendency to separate a visual display into figure and ground. One part is depicted as Figure and the other as Ground. cogch2

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35. Gestalt Principles of Perceptual Organization Law of Pragnanz (good form or simplicity) cogch2

36. 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 cogch2

37. Similarity occurs when objects look similar to one another. People often perceive them as a group or pattern. The example above (containing 11 distinct objects) appears as single unit because all of the shapes have similarity. cogch2

38. Good Continuation: Group together items that follow in a straight or smooth line. Common Fate cogch2

39. 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. cogch2

40. 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 cogch2

41. 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. cogch2

42. 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 A A cogch2

43. 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). cogch2

44. Many things we can readily distinguish have very similar shapes. cogch2

45. Feature Analysis or Detection: break objects down into features and match against stored object features. cogch2

46. 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”. cogch2

47. Video cogch2

48. Feature detectors are neurons that respond to specific features of the environment, such as lines, orientation, edges (end-stops), and movement. cogch2

49. 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. cogch2

50. 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. cogch2