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Psychology of Perception & Attention

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Psychology of Perception & Attention

  1. 1. Perception
  2. 2. Perception is the an active process by which the cognitive system construct an internal representation of outside world
  3. 3. Perception external environment presentation outside world Perception our personal experience of our sense pick up
  4. 4.  Perception is not accurate perception of reality  It is interpretation of sensory input  Senses may deceive us
  5. 5. What do we perceive with? Senses
  6. 6. we perceive with senses by organ sense Electromagnetic waves of certain frequencies eyes Vision 1 Waves of air pressure; air vibrations ears audition 2 chemical substances tongue taste 3 chemical substances nose smell 4 Pressure of skin skin touch 5 Balance ear Equilibrioception 6 temperature skin thermoception 7 pain all nociception 8
  7. 7. Physiology of Perception
  8. 8. Physiology of perception Physical input Action potential stimulus sensor
  9. 9. Primary visual cortex
  10. 10. From sensation To perception Light retina Rods &cons Neural activity bottom up processing
  11. 11. bottom up processing
  12. 12. H Expectation & previous knowledge A A H
  13. 13. Physiology of perception, top down processing Expectations, Emotions Previous knowledge etc “high level” brain areas ;  Prefrontal cortex  Superior parietal cortex influences neural processing in lower perceptual areas
  14. 14. Top-down modulation Bottom-up processing Perception
  15. 15. To sum-up physiology of perception Physical stimulus  Receptor  Neural activity activation of sensory brain areas Sensory processing in neocortex Highly organized District areas for colors, motion, form,…. Hierarchical Goes from simple to complex Top-down influences Context, Expectations, knowledge, etc. influence perception
  16. 16. Psychophysics
  17. 17. Which square is brighter? Perception does not mirror reality, it may distort it. Psychophysics: how does perception actually capture reality, It is the Relation between physical stimuli and their perception
  18. 18. Psychophysics Absolute threshold (detection threshold) Relative threshold (noticeable difference)
  19. 19. Psychophysics What is minimum strength of physical stimulation so that we notice its presence Affected by motivation, expectation, attention, adaptation Absolute threshold (detection threshold)
  20. 20. Psychophysics Absolute threshold (detection threshold)
  21. 21. Smallest detectable difference between two stimuli Relative threshold (noticeable difference)
  22. 22. Relative threshold (noticeable difference) Psychophysics
  23. 23. How to benefit from relative threshold Reduce size Reduce weight Reduce quality Increase price Negative changes Positive changes Discount Increase size Better package
  24. 24. Gestalt Theory
  25. 25. Gestalt Theory Gestalt [ɡəˈʃtalt] "shape, form" the mind forms a global whole with self-organizing tendencies
  26. 26. • Principle of totality • One should investigate the whole percept, i.e. taking into account all possible parts Gestalt Theory
  27. 27. Gestalt Theory  Law of Prägnanz; People will perceive and interpret ambiguous or complex images as the simplest form(s) possible We prefer things that are simple, stable, clear and ordered. This is the fundamental principle of gestalt  Laws of grouping Law of Simplicity
  28. 28. Gestalt Theory • Law of proximity Objects close together form a group
  29. 29. Gestalt Theory  Law of Similarity Similar visual elements form a group
  30. 30. Gestalt Theory  Law of Closure Objects are perceived as whole even if they are not complete
  31. 31. Gestalt Theory  law of symmetry Objects symmetrical around a center point from a group symmetry vs proximity
  32. 32. Gestalt Theory  law of continuity We tend to perceive objects as forming smooth continuous patterns
  33. 33. Gestalt Theory  law of figure and ground segregation We tend to structure the visual field into parts: A figure and ground Bistable percepts Monostable percepts
  34. 34. the mind forms a global whole with self-organizing tendencies Law of Prägnanz; People will perceive and interpret ambiguous or complex images as the simplest form(s) possible Proximity Similarity Closure Symmetry Continuity figure and ground segregation
  35. 35. Depth perception
  36. 36. Depth perception  Localizing objects in a 3-dimentional world  The world is projected onto the eye as two-dimensional images (2 photo)  But how? How to create 3D percept from two two-dimensional images?
  37. 37. cues Binocular cues (information from both eyes) monocular cues (information from one eyes)
  38. 38. Binocular cues Binocular cue 1 “Binocular disparity”  The eyes view the world from a different angle • The main cue in 3D movies; present different picture to the left and right eye
  39. 39. Binocular disparity • The main cue in 3D movies; present different picture to the left and right eye The 2 picture are colour coded  glasses with colour filters The 2 picture are presented alternatively; LCD shutter glasses block the eye in the correct rhythm The 2 picture are presented with light of different polarization; The glasses act as polarization filter Binocular cues
  40. 40. Binocular cue 2 “convergence”  The two eyes move inward for near objects to focus the object  Eye muscles provide information on convergence Binocular cues
  41. 41. cues Binocular cues (information from both eyes) monocular cues (information from one eyes)
  42. 42. monocular cue 1 Occlusion  An object partly hidden by another object must be behind it Monocular cues
  43. 43. monocular cue 2 Texture gradient  The texture of objects changes with distance Monocular cues
  44. 44. monocular cue 3 Motion Parallax  When moving, distant objects move slower Monocular cues
  45. 45. Depth perception Mind construct a 3D representation from two 2D images by using:  Binocular cues  Monocular cues disparity convergence occlusion Texture gradient Motion parallax
  46. 46. Object Recognition
  47. 47. Object Recognition Basic stages of object recognition  Stage 1 Processing of basic object components, such as colour, depth, and form.  Stage 2 These basic components are then grouped on the basis of similarity, providing information on distinct edges to the visual form. Subsequently, figure-ground segregation is able to take place.  Stage 3 The visual representation is matched with structural descriptions in memory.  Stage 4 Semantic attributes are applied to the visual representation, providing meaning, and thereby recognition.
  48. 48. Object Recognition Hierarchical recognition processing Visual recognition processing has been typically viewed as a bottom-up hierarchy in which information is processed sequentially with increasing complexities, where lower-level cortical processors, such as the primary visual cortex, are at the bottom of the processing hierarchy and higher-level cortical processors, such as the inferotemporal cortex (IT), are at the top, where recognition is facilitated. A most recognized bottom-up hierarchical theory is David Marr's theory of vision
  49. 49. Disorders of Perception
  50. 50. Disorders of perception  Perceptual loss Visual agnosia (inability to recognize images with intact vision), Alexia (inability to recognize written material with intact vision and previous knowledge)  Perceptual distortion Micropsia (objects appear smaller) macropsia (objects appear larger), hyperacusis (sounds are louder) hypoacusis(sounds are softer)  Perceptual deception Illusions: misinterpretation of existing stimuli, e.g. seeing a rope as a snake. Hallucinations: perception in the absence of external stimuli.
  51. 51. Attention
  52. 52. The process by which we select some stimuli for further processing while ignoring others Attention
  53. 53. Involuntary attention Types of Attention Voluntary attention Spontaneous attention
  54. 54. factors attracts attention
  55. 55. factors attracts attention External Internal
  56. 56. External factors Pizza Type of stimulus Position of stimulus Contrast of stimulus Changeability & repetition of stimulus
  57. 57. Internal factors Mental set Biological needs
  58. 58. 2 What is OCD Epidemiology Nosology Symptoms Diagnosis OCPD Vs. OCD Investigations Etiology Treatment Questions Terms ‫يحبذ‬ ‫حسين‬
  59. 59. Further reading
  60. 60. www.facebook.com/MaamouraTA www.nafsy.net /nafsy.net @nafsyclinic @nafsyclinic