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1 perceptual process

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1 perceptual process

  1. 1. Cognition (mental activity or mental processes) Cognition (Latin: cognoscere, "to know" or "to recognize") refers to the acquisition, storage, transformation, and use of knowledge. Cognition can be natural or artificial, conscious or unconscious. It is a faculty of mental processes such as learning, memory, perception, thinking, problem solving, reasoning, decision making etc.
  2. 2. Characteristics The cognitive processes are active, rather than passive The cognitive processes are remarkably efficient and accurate The cognitive processes Handle positive information better than negative information The cognitive processes are interrelated with one another, they do not operate in isolation many cognitive processes rely on both bottom- up and top-down processing
  3. 3. Sensation and Perception Sensation The processes by which our sense organs receive information from the environment. Transduction The process by which physical energy is converted into sensory neural impulses. Perception The processes by which people select, organize, and interpret sensations.
  4. 4. Sensation & Perception Processes
  5. 5. sensation Sensation is defined as: Irreducible elements from which perceptions are formed as experiences which are simpler and less meaningful than perceptions and uninfluenced by learning and other psychological processes such as emotion and motivation (Hebb, 1972; Scharf, 1975).
  6. 6. Problems of perception No direct physical contact with the visual elements is required to appreciate there nature. How do we form the impressions of the quantitative and qualitative aspects of external objects? Does the real physical world actually exist independently of our experience? If so, how we can come to know its properties and how truth of that knowledge be determined?
  7. 7. Problems… How percepts are constructed from the interaction of physical energy (light) and the perceiving organism. Proximal and distal stimuli are different but our perceptions are generally accurate or veridical enough to adjust ourselves in the environment. Some times percept have properties considerably different form proximal stimulus.
  8. 8. Components of perception Distal stimulus Distal stimulus refers to a physical aspect of the external environment, or the physical energy which comes from the eternal source. For example, object in the external environment such as, table, fan etc. Proximal stimulus It refers to the physical energy coming from the external source strikes on the sensory receptors.
  9. 9. Components… Input and output Input refers to the sensation of stimulus and output refers to behavior made in response to the input. Percept Out come of perception is known as percept. Recognizing an object as flower would be an example of percept.
  10. 10. Difference between proximal and distal stimulus Much of the light coming form distal source is scattered by molecules and lost before it reaches the receptors of the eye. Resulting proximal image is much smaller, inverted relative to the distal stimulus Proximal stimulus is partly under the control of observer’s head and eye movements. Information in the form of electromagnetic energy is changed in the neural impulses (transduction).
  11. 11. Defining perception According to Morgan and King, “perception is the way the world look (sounds, feels, tastes and smells too)”. According to Zigher (1985), perception refers to the interpretation of sensory information, as a constructive and creative process which endows sensory experience with meaning.
  12. 12. Defining… Perception is a process by which individuals organize and interpret their sensory impressions in order give meaning to their environment for making better adjustment with it. Perception is a process by which we recognize and interpret or give meaning to raw material provided by sensory system with the help of other psychological processes such as, learning, memory, emotions and motivation.
  13. 13. Defining… Perception is the process of creating an internal representation of the out side world (internal representation is a joint product of bottom up and top-down processing). Perception is the interpretation of the information provided by sensory system.
  14. 14. Perception is active, selective and relatively more automatic higher mental process through which we experience or interpret our immediate surrounding.
  15. 15. Properties of perception Perception is interpretation of physical energy or giving meaning to it. In perception, registered stimuli by the senses are gathered and interpreted with the help of previous knowledge. Perception combines aspect of both the outside world (the stimulus) and inner world (previous knowledge).
  16. 16. Properties … Perception is relatively more automatic process, required less effort than other cognitive tasks, such as problem solving of decision making. Perception is influenced by other psychological processes such as motivation and emotion. Perception is an active mental process involves both top-down and bottom-up processing.
  17. 17. Concepts in perception Physical- external or internal stimulus such as wave length, intensity etc. Physiological- stimulation of sensory system: neural activity- excitation- inhibition; sensory modality: transduction Behavior Subjective experience
  18. 18. Perception Perceptual Organization Perceptual Constancies Depth and Dimension Perceptual Set The World of Illusions
  19. 19. Approaches to perception Structuralism Wilhelm Wundt and Edward Bradford Titchner (1867-1927) Structuralisms emphasized on the study of the structure of perception. Its goal was to uncover the simplest, most basic elements of conscious experience (bottom-up processing).
  20. 20. Constructivist Approach Emphasized on the active nature of perceptual process. Influenced by empiricism. Proposed that the percept is more than the information coming form stimulus. Some constructive processes occur within the observer. These are mediating processes between physical world and its perception. Our perception is a mental construction based on our cognitive strategies, past experiences, biases, expectations, motives, attention, and other personal characteristics
  21. 21. Direct perception approach (James J. Gibson, 1904-1979) Stimulus contains important information necessary for perception Past experiences are not important Perception depends on the characteristics of stimuli (subjective variables are not important) It is also known as ecological approach because it focuses on the adaptive link between the perceiving organism to its physical environment.
  22. 22. Computational Approach (David Marr, 1945-1980) Involves mathematically oriented analysis of certain aspects of visual perception derived form computer simulation and AI. Accepts Gibson’s basic idea of direct perception but also proposes that perception of characteristics such as lines, edges, borders, contours, motion, and other discontinuity.
  23. 23. Beliefs of the information-processing approach Information is processed in stages Information is processed serially The nature of information changes stage to stage Information processing is affected by several factors (noise) It uses both bottom-up and top-down processing It is a mediating process between input and output
  24. 24. Gestalt approach (German: Gestalt - "shape" or "figure") Berlin School Kurt Koffka, Max Wertheimer, and Wolfgang Köhler (students of Carl Stumpf) are the founder of this school. The 'Gestalt' or 'whole form' approach sought to define principles of perception -- seemingly innate mental laws which determined the way in which objects were perceived.
  25. 25. Gestalt: Basic idea Operational principle of the brain is holistic, parallel, and analog, with self-organizing tendencies “The whole is greater than the sum of the parts" Opposed to structuralism and Wundt Gestalt effect refers to the form-forming capability of our senses particularly visual sense.
  26. 26. Figure and ground Properties of figure ground Figures hold more memorable association than the ground. Figures are seen as being in front of the ground. The ground is seen as uniformed material and seems to extend behind the figure. The contour separating the figure from the ground appears to belong to the figure. Compared to ground, perception of figure is effortless
  27. 27. Field forces Cohesive forces Restraining forces ∑ C = ∑ R = no perception (Ganzfeld) ∑ C > ∑ R = perception ∑ C < ∑ R = unclear or unstable perception
  28. 28. Laws of pragnanz The fundamental principle of gestalt perception is the law of prägnanz (German for pithiness). The physiological organization will always be good. Good refers to the simplest and most stable. We tend to order our experience in a manner that is regular, orderly, symmetric, and simple.
  29. 29. Gestalt laws of perceptual organization Gestalt psychologists modified Law of prägnanz and given laws which hypothetically allow us to predict the interpretation of sensation. These laws are called "gestalt laws".
  30. 30. Figure-ground
  31. 31. Perceptual Organization Reversible Figures Drawings that one can perceive in different ways by reversing figure and ground. Gestalt Psychology School of thought rooted in the idea that the whole is different from the sum of its parts.
  32. 32. Camouflage Importance of contour
  33. 33. Perceptual Organization Gestalt Laws of Grouping Proximity Seeing 3 pair of lines in A Similarity Seeing columns of orange and red dots in B Continuity Seeing lines that connect 1 to 2 and 3 to 4 in C Closure Seeing a horse in D
  34. 34. Gestalt Perceptual Psychology Laws of Perceptual Organization Law of Similarity
  35. 35. Gestalt Perceptual Psychology Laws of Perceptual Organization Law of Proximity (nearness)
  36. 36. General Perceptual Psychology Principles of Perceptual Organization The principle of common region
  37. 37. General Perceptual Psychology Principles of Perceptual Organization The principle of common region
  38. 38. General Perceptual Psychology Principles of Perceptual Organization The principle of connectedness
  39. 39. General Perceptual Psychology Principles of Perceptual Organization The principle of synchrony (objects that change together are grouped together)
  40. 40. General Perceptual Psychology Principles of Perceptual Organization Repetition Discrimination Task - groupings influence perception and speed of search:
  41. 41. Perceptual Segregation Figure-ground segregation-We are primed to see a figure in front of a background Symmetry and perception of figure and ground
  42. 42. Perceptual Segregation Figure-ground segregation-We are primed to see a figure in front of a background Area size and perception of figure and ground
  43. 43. Perceptual Segregation Figure-ground segregation-We are primed to see a figure in front of a background Orientation and perception of figure and ground
  44. 44. Perceptual Segregation Figure-ground segregation-We are primed to see a figure in front of a background Meaningfulness and perception of figure and ground
  45. 45. Pattern recognition Pattern recognition and attention prepare the raw sensory information for more complex mental process. Pattern recognition allows us to perceive a form in a stimulus and attention is responsible for our more extensive processing of some information. Pattern recognition is the identification of complex arrangement of sensory stimuli.
  46. 46. In pattern recognition raw information is organized and transformed by sensory process and compared with information in other memory storage. Thus, pattern recognition involves realizing that a particular pattern is seen before.
  47. 47. Bottom up processing (Data driven) • emphasizes importance of stimulus in PR. • Information coming from the stimulus is enough to recognize the pattern. • Recognition process in initiated by the parts of the pattern which serves as the basis for the recognition of whole.
  48. 48. Top down processing (conceptually driven) Emphasizes that concept and high level of processing influence PR. Our knowledge about the world help us identifying patterns. The process of PR is initiated by a hypothesis about the whole leading to the identification of whole and the subsequent recognition of components.
  49. 49. Bottom up models of perception
  50. 50. How do we recognize patterns? Do we identify an object because we have first recognize it’s components or do we recognize these part because we have first identified the object? The problem that, whether the recognition process is initiated by the parts of the pattern or whether it is initiated by a hypothesis about the whole (hypothesis testing) is called prasing paradox.
  51. 51. A: Template Matching Theory Templates are specific patterns that are stored in memory. Stimulus is compared with a set of templates. We recognize the stimulus as the template that matches most closely. Stimulus must fit the template precisely.
  52. 52. Problems of TMT If a number of templates match or come close (not one)- We need further processing to sort out which template is most appropriate which will take much time than it actually takes. It does not explain how perception works. with the development of technology our experiences change thus, how and when templates are created?
  53. 53. How different patterns are recognized as same despite the wide variation in the size, shape, orientation etc. (e.g. recognizing hand writing of different people). It works for simple latter and simple objects.
  54. 54. B: Feature Analysis Feature analysis model assumes that instead of processing stimuli as whole units, we break them down into their components. We recognized those parts to infer what the whole represents. There is physiological mechanism in retina and in the cortex. These are called feature detectors. Some cells respond to boarders between light and dark called edge detectors. Movement detectors are called bug detectors. Horizontal and vertical line detectors are also found in the cortex.
  55. 55. 1: Distinctive feature approach Discrimination among letters is made on the basis of small no of characteristics called distinctive features. We store a list of feature components for each letter. E.g. Q has a round closed shape and a diagonal line. Gibson (1969) demonstrated that people require long time to decide whether some letters are different from one another when the letter share large number of critical features.
  56. 56. For example, P and R are similar on a large number of critical features; and G and M are different from each other on a large number of critical features. Differentiation between G and M takes less time as compared to differentiation between P and R. In distinctive feature approach pattern recognition involves detecting specific important parts while in TMT emphasizes prototype and entire recognition of entire shape.
  57. 57. Problems of distinctive feature approach Explain simple shape or features recognition such as letter recognition. It does not explain physical relationships. For example, T and L are similar but they are recognize distinctly on the basis of relationship. For example, T has a vertical line supports a horizontal line in the middle. Where L has the vertical line rests at the side of the horizontal line. It explains simple letter recognition but natural features, shapes are more complex. How can we recognize a horse?
  58. 58. 2: The Computational Approach (David Marr (1982) Images- Identification of object’s edges by combining intensity of the image Primal sketch- edges are organized into abstract representation 2 ½ D sketch- primal sketch is converted into 2 ½ D sketch (contours, shade, rough depth) 3 D image- Describes shapes and their spatial organization of the object.
  59. 59. Perceptual Organization Identifying Objects Geons (geometric icons) are simple 3D component shapes. A limited number are stored in memory. Geons are combined to identify essential contours of objects.
  60. 60. Perceptual Constancies Size Constancy The tendency to view an object as constant in size despite changes in the size of the retinal image. Shape Constancy The tendency to see an object as keeping its form despite changes in orientation.
  61. 61. Perceptual Constancies The Ames Room A specially-built room that makes people seem to change size as they move around in it The room is not a rectangle, as viewers assume it is. A single peephole prevents using binocular depth cues.
  62. 62. Perceptual Constancies Shape Constancy Even though these images cast shadows of different shapes, they still are seen as round.
  63. 63. Perceptual Constancies Size Constancy Tendency to view an object as constant in size despite changes in the size of the retinal image. http://www.psychologie.tu-dresden.de/i1/kaw/diverses%20Material/www.illusionworks.com/assets/images/constancy.jpg
  64. 64. Depth Perception: Binocular Depth Cues
  65. 65. Binocular Cues Depth cues that require the use of both eyes Enables people to see in three dimensions.
  66. 66. Retinal Disparity A binocular depth cue resulting from slightly different images produced by the separation of the retinas in the left and right eye Is most effective when the item is quite close to the person
  67. 67. Binocular Depth Cues: Finger Sausage
  68. 68. Retinal Disparity Text example page 189
  69. 69. Autostereograms
  70. 70. Retinal Disparity Demo 1. Roll a piece of scrap paper into a tube shape. 2. Hold it to your right eye as if it were a telescope 3. Look through the tube focusing on an object on a blank wall in front of you. 4. Keeping both eyes open, hold your open left hand beside the tube…continue to focus on the object on the wall. 5. The images should fuse and ….
  71. 71. Convergence A binocular depth cue related to the tension in the eye muscles when the eyes track inward to focus on objects close to the viewer The more tension in the eye muscle, the closer the object is Works best at close distances
  72. 72. Monocular Cues Depth cues that require the use of only one eye
  73. 73. Components of Monocular Cues Monocular depth cues include: 1.relative size 2.relative motion 3.interposition 4.relative height 5.texture gradient 6.relative clarity 7.linear perspective
  74. 74. Monocular Depth Cues 1. Relative Size Using the perceived size of a familiar object to determine depth The larger the object appears, the closer the object is to the viewer
  75. 75. Monocular Depth Cues 2. Relative Motion A person who is moving can determine depth by focusing on a distant object. Objects further away than the object of focus will appear to move in the same direction as the subject is moving. Objects closer than the object of focus will appear to move in the opposite direction.
  76. 76. Relative Motion Illustration
  77. 77. Monocular Depth Cues 3. Interposition Method of determining depth by noting that closer objects partially obstruct the more distant objects Also called “overlap”
  78. 78. Monocular Depth Cues 4. Relative Height Method of determining depth by noting that distant objects appear higher in your field of vision than do closer objects
  79. 79. Monocular Depth Cues 5. Texture Gradient Method of determining depth by noting that distant objects have a smoother texture than nearby objects Can see individual blades of hay, but in the Distance, the hay seems to have a smoother Texture.
  80. 80. Monocular Depth Cues 6. Relative Clarity Method of determining depth by noting that distant objects are less clear than nearby objects Tends to work Paris Street: A Rainy Day by Gustave outdoors Caillebotte
  81. 81. Monocular Depth Cues 7. Linear Perspective Method of determining depth by noting that parallel lines appear to converge in the distance As parallel lines become more The lines appears to distant from us, they appear to get closer together - like the sides of eventually merge on the gray bit at left. Their the horizon. apparent closeness is therefore a cue to their relative distance from us.
  82. 82. Depth and Dimension 8.The Visual Cliff Devised by Eleanor Gibson and Richard Walk to test depth perception in infants and animals. Provides visual illusion of a cliff. Caregiver stands across the gap. Babies are not afraid until about the age they can crawl.
  83. 83. Perceptual Set What is seen in the center figures depends on the order in which one looks at the figures: If scanned from the left, a man’s face is seen. If scanned from the right, a woman’s figure is seen.
  84. 84. Perceptual Set Context Effects The same physical stimulus can be interpreted differently depending on perceptual set, e.g., context effects. When is the middle character the letter B and when is it the number 13?
  85. 85. The World of Illusions The Müller-Lyer Illusion Illusion in which the perceived length of a line is altered by the position of other lines that enclose it
  86. 86. The World of Illusions The Ponzo Illusion Illusion in which the perceived line length is affected by linear perspective cues. Side lines seem to converge Top line seems farther away But the retinal images of the red lines are equal.
  87. 87. The Continuing Controversy The ganzfield procedure Researchers disagree about the reliability of studies done to replicate the ganzfield test. Visit www.randi.org/ for information about the James Randi Educational Foundation’s million-dollar paranormal challenge.

Notes de l'éditeur

  • Sensation &amp; Perception 10/10/12 ©2001 Prentice Hall
  • Sensation &amp; Perception 10/10/12 ©2001 Prentice Hall Figure 3.2 from: Kassin, S. (2001). Psychology , third edition. Upper Saddle River, NJ: Prentice Hall.
  • Sensation &amp; Perception 10/10/12 ©2001 Prentice Hall Section outline
  • Sensation &amp; Perception 10/10/12 ©2001 Prentice Hall Figure 3.20 (lady/girl) and 3.21 (rabbit/duck) from: Kassin, S. (2001). Psychology , third edition. Upper Saddle River, NJ: Prentice Hall. Quote from: Shephard, R. N. (1990). Mind Sights . New York: W. H. Freeman.
  • Sensation &amp; Perception 10/10/12 ©2001 Prentice Hall Figure 3.23 from: Kassin, S. (2001). Psychology , third edition. Upper Saddle River, NJ: Prentice Hall.
  • Sensation &amp; Perception 10/10/12 ©2001 Prentice Hall Figure 3.25 from: Kassin, S. (2001). Psychology , third edition. Upper Saddle River, NJ: Prentice Hall. Source: Biederman, I. (1987). Recognition-by-components: A theory of human image understanding. Psychological Review, 94 , 115-147.
  • Sensation &amp; Perception 10/10/12 ©2001 Prentice Hall Figure 3.25 from: Kassin, S. (2001). Psychology , third edition. Upper Saddle River, NJ: Prentice Hall.
  • Sensation &amp; Perception 10/10/12 ©2001 Prentice Hall Figure 3.26 from: Kassin, S. (2001). Psychology , third edition. Upper Saddle River, NJ: Prentice Hall.
  • Perceptual constancies – perception of entire object does not change, even though some of the sensory items have changed Size Constancy Tendency to view an object as constant in size despite changes in the size of the retinal image. Wundt had no way to explain why this happened either, just like the phi phen.
  • Sensation &amp; Perception 10/10/12 ©2001 Prentice Hall Figure 3.27 from: Kassin, S. (2001). Psychology , third edition. Upper Saddle River, NJ: Prentice Hall.
  • Sensation &amp; Perception 10/10/12 ©2001 Prentice Hall Figure 3.28 from: Kassin, S. (2001). Psychology , third edition. Upper Saddle River, NJ: Prentice Hall.
  • Sensation &amp; Perception 10/10/12 ©2001 Prentice Hall Figure 3.29 from: Kassin, S. (2001). Psychology , third edition. Upper Saddle River, NJ: Prentice Hall.
  • Sensation &amp; Perception 10/10/12 ©2001 Prentice Hall Figure 3.32 from: Kassin, S. (2001). Psychology , third edition. Upper Saddle River, NJ: Prentice Hall.

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