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Sensation and perception

  1. 1. CHAPTER TWO Sensation and perception1 SENSATION AND PERCEPTION
  2. 2. 2.1. Introduction Sensation and perception2 Sensation: process of detecting, converting, & transmitting raw sensory information from the external & internal environments to the brain  Stimulus (pl stimuli): specific energy needed to stimulate sense organs.  Distal stimulus: the real object in the external world.  Proximal stimulus: representation of the physical reality
  3. 3. Sensation and perception3  Perception: process of selecting, organizing, & interpreting sensory information into meaningful patterns
  4. 4. Sensation Vs. Perception Sensation and perception4
  5. 5. 2.2. Sensation Sensation and perception5  Processing: Our five senses (vision, audition, etc.) have special receptors (e.g., eye’s rods & cones), which detect & transmit sensory 2.2.1. Sensory Data Processing2.2.1. Sensory Data Processing
  6. 6. Sensation and perception6 Four Forms of Sensory Data Processing: 1. Sensory detection: eyes, ears, other sense organ contain receptor cells that detect & process sensory information 2. Transduction: converts receptor’s energy into neural impulses that are sent on to the brain 3. Coding: converting sensory inputs into different sensations 4. Sensory Reduction: filtering and analyzing incoming sensations before sending neural messages on to the cortex
  7. 7. Sensation and perception7 Neural impulses from sensory receptors in our eyes, ears, skin, & other sensory organs create neural messages
  8. 8. 2.2.2. Psychophysics and Signal Detection Sensation and perception8  Psychophysics: studies the link between physical characteristics of stimuli and our sensory experience  Absolute Threshold: smallest amount of a stimulus we can reliably detect 50% of the time.  Difference Threshold: minimal difference needed to detect a stimulus change; also called the “just noticeable difference” (JND).
  9. 9. Absolute threshold Sensation and perception9 Proportionof“Yes”Responses 0.000.501.00 0 5 10 15 20 25 Stimulus Intensity (lumens)
  10. 10. Sensation and perception10 Weber’s absolute threshold examples
  11. 11. Sensation and perception11
  12. 12. Stimulus vs Response Sensation and perception12 Physical world Psychological experience Light Brightness Sound Volume Pressure Weight Sugar Sweet
  13. 13. Sensation and perception13 Weber’s law: states that just noticeable difference (jnd) is proportional to the intensity of the original stimulus. JND(k)=∆I/I or ∆I=Ixk  Fechner’s law: states that perception changes linearly as the stimulus changes geometrically. Perceptual intensity= k*log physical intensity. S=K log I
  14. 14. Sensation and perception14
  15. 15. Sensation and perception15  Ex: If I increases from 100 to 200, the psychological experience will be:  S=K log I S=0.1 log 50 =0.1*1.7=0.17 S=0.1 log 100=0.2
  16. 16. Sensation and perception16
  17. 17. Subliminal perception Sensation and perception17 Subliminal perception: When we detect stimuli that are below our absolute threshold for conscious awareness. Subliminal (or below the threshold) message for one person, may be supraliminal (above the threshold) for another person.
  18. 18. Sensation and perception18
  19. 19. Signal Detection Theory Sensation and perception19  This theory states that detection of a stimuli depend on physical, psychological and environmental factors.
  20. 20. Signal detection decision matrix Sensation and perception20 Stimulus present Participant’s Response Yes No Yes Hit False alarm No Miss Correct rejection  Hit: true positive  Miss: False negative  False alarm: false positive Correct rejection: true negative
  21. 21. Measurements in psychophysics Sensation and perception21 • Reaction time (RT) as DV • Method of limits: the respondent is asked to answer or judge change or presence of stimuli in different series (ascending or descending) • Method of constant stimuli: stimuli of varying intensity are presented in random order. • Method of adjustment/average error: subjects adjust the stimulus level upward or downward the standard.
  22. 22. Understanding Sensation Sensation and perception22 Sensory Adaptation: decreased sensitivity due to repeated or constant stimulation
  23. 23. 2.2.3. Vision Light is a form of electromagnetic energy that moves in waves. • Various types of electromagnetic waves form the electromagnetic spectrum. Sensation and perception23
  24. 24. The eye vs camera Sensation and perception24
  25. 25. Sensation and perception25
  26. 26. Electromagnetic Spectrum Sensation and perception26  The flower on the left is what we normally see. The one on the right, photographed under ultraviolet light, is what we think most animals & insects see.
  27. 27. Light Waves Sensation and perception27
  28. 28. Sensation and perception28  Wavelength: distance between the crests (or peaks)  Frequency: how often a light or sound wave cycles  Amplitude: height of a light or sound wave
  29. 29. Electromagnetic Spectrum Sensation and perception29
  30. 30. How We See: Anatomy of the Eye  The function of the eye is to capture light waves and focus them on receptors at the back of the eyeball. Sensation and perception30
  31. 31. Structures of the Retina • Receptors for vision are the rods: sensitive to light & cones (for dim color) located in the retina. Sensation and perception31
  32. 32. Sensation and perception32
  33. 33. Sensation and perception33  Vision research helps explain how the shape of your eyeball creates two common visual problems  Nearsightedness: inability to see far objects.  Farsightedness.: inability to clearly see near objects.
  34. 34. Sensation and perception34  Color vision is a combination of two theories 1. Trichromatic Theory: color perception results from three types of cones in the retina, sensitive to either red, green, and blue Theories of Color Vision
  35. 35. Sensation and perception35 2. Opponent-Process Theory: two different receptors(cons) sensitive for opposite colors (blue-yellow, red- green, & black-white).  The activation of one color suppresses the other complementary color.
  36. 36. Sensation and perception36 • How does the opponent- process theory help explain the effects of the “spiral illusion”?
  37. 37. Sensation and perception37  Are you “color blind”? People who have red- green color deficiency have trouble perceiving the green colored number in the center of this circle.
  38. 38. 2.2.4. Audition • Sound results from movement of air molecules in a particular wave pattern. • Sound waves vary in: • wavelength, which determines pitch (highness or lowness). • amplitude, which determines loudness (intensity of the sound). Sensation and perception38
  39. 39. Sensation and perception39
  40. 40. Theories of Pitch Perception Sensation and perception40  Place Theory: pitch perception is linked to the particular spot on the cochlea’s basilar membrane that is most stimulated.  Frequency Theory: pitch perception occurs when nerve impulses sent to the brain match the frequency of the sound wave.
  41. 41. Measuring Audition • The loudness of a sound is measured in decibels. Constant noise above 90 decibels can cause permanent nerve damage & irreversible hearing loss. Sensation and perception41
  42. 42. 2.2.5. Olfaction  Olfaction: sense of smell  Receptors for smell are embedded in the nasal membrane (the olfactory epithelium). Sensation and perception42
  43. 43. 2.2.6. Gustation (Sense of Taste)  Gustation refers to sense of taste responding to different chemicals.  There are about 10,000 receptors for taste (taste buds), located in papillae on the surface of the tongue. Sensation and perception43
  44. 44.  The following are the basic tastes:  Sweet (Sucrose)  Bitter (quinine)  Salty (Sodium chloride)  Sour (HCL)  People perceive salty tastes most rapidly and bitter tastes least rapidly.  Women are more sensitive to taste (have more taste buds) compared to men. Sensation and perception44
  45. 45. 2.2.7. Body Senses Sensation and perception45  A. Skin senses involve three skin sensations-- touch (or pressure), temperature, & pain.  Receptors for these sensations occur in various concentrations & depths in the skin.
  46. 46. Sensation and perception46  B. Vestibular sense (or sense of balance) involves the vestibular sacs & semicircular canals located within the inner ear.
  47. 47. C. Kinesthesia provides our brains with information about posture, orientation, and movement.  Kinesthetic receptors are located in muscles, joints, and tendons. Sensation and perception47
  48. 48. 2.3. Perception  Perception: the set of processes by which we recognize, organize, and make sense of the sensations we receive from environmental stimuli. It is understanding and giving meaning to sensation.  There are three processes in perception  Selection  Organization interpretation  Extra-sensory perception Sensation and perception48
  49. 49. 2.3.1. Selection  There are are three main processes in selection (choosing where to direct attention) involves:  Selective attention: filtering out and attending only to important sensory messages  Cocktail-party phenomenon  Feature detectors: specialized neurons that respond only to certain sensory information  Habituation: brain’s tendency to ignore environmental factors that remain constant Sensation and perception49
  50. 50. Theoretical Approaches to Perception 1. Direct Theories [Bottom-Up Approaches] • Claim that perception starts from “the bottom” (physical stimuli) then progress to the brain for higher-level cognitive processes. • Look at Gibson’s theory of direct perception Sensation and perception50 This stimulus will be broken down into specific features by the brain to be perceived as a letter “B.”
  51. 51.  The bottom-up approach states :we have feature detectors(specialized neurons) that respond to the presence of certain simple features, such as angles and vertical and horizontal lines, and curves. Sensation and perception51
  52. 52. Gibson’s Theory of direct perception  Acc. J. Gibson the array of information in our sensory receptors, including sensory context, contains every thing needed for perception  The movement of the observer is essential  We do not need higher cognitive processes or anything else to mediate between our sensory experiences and our perceptions  Existing beliefs or higher-level inferential thought processes are not necessary for perception Sensation and perception52
  53. 53. The optic array  The optic array: the light structured by the presence of objects, textures, and objects changes depending up on the position and movement of the person.  Sources of information invariation  Texture gradient: when near objects appear coarse  Flow pattern: when objects appear to move past a moving observer  Horizon ratio: when objects are cut by a horizon Practical contribution  parallel lines painted on roads, and illumination can enhance perception Sensation and perception53
  54. 54. 2. Top-Down Approaches State that information processing starts “at the top” with higher-level mental processes (based on experiences and expectations) and then work down.  Perceptual set: Allport’s term for predispositions and expectations in perception can serve as a best example of this approach. Sensation and perception54
  55. 55.  These two letters are perceived based on our experiences than their specific features Sensation and perception55
  56. 56.  Generally, top down approaches states perception is constructed based on:  Schemata:  Priming: previous information (stored in memory)  Cognition  Expectation  Perceptual set  Context Sensation and perception56
  57. 57. Attention  Attention: focusing on a limited range of stimuli or event.  Selective attention: focusing on a specific aspect of experience while ignoring others.  Cocktail- party- phenomenon: when you give attention to a person who calls your name in a crowded room.  . Factors that increase attention  Novelty  Size  Color  Movement  Interest  Frequency Sensation and perception57
  58. 58. “The Stroop Effect” (Part A.)
  59. 59. “The Stroop Effect” (Part B.)
  60. 60. “The Stroop Effect” (Part C.)
  61. 61. “The Stroop Effect” Why is it more difficult to name the colors in “Part C.?”  The “Stroop Effect” illustrates how difficult it is to ignore some kinds of stimuli  You were receiving two stimuli – the color and the word – which compete and slow you down when you try to name the color
  62. 62. 2.3.2. Perceptual organization  The process of assembling perceptual data in order to make them meaningful.  For example, organizing perceived colors and lines into objects  Perceptual organization involves:  Shape perception  Perceptual constancy  Depth perception Sensation and perception62
  63. 63. A. Shape Perception  Shape perception involves perceiving shapes, forms, and patterns. a. Figure-Ground Relationship  Perceiving the figure (the stimulus) from the left out surrounding (background) Sensation and perception63
  64. 64. Sensation and perception64
  65. 65. b. Gestalt laws of perception  Gestalt: a german word for pattern, form and configuration  The laws are:  The law of closure: incomplete figures as a whole Sensation and perception65
  66. 66. Proximity: objects that are near each other tend to be perceived as a unit PPP PPP PPD Similarity: we tend to group similar items (in terms of color, shape, size) together CCCCBBBDDD D. Good continuation perceiving patterns as continuing even though they are disrupted, or discontinued. Sensation and perception66
  67. 67. Common fate: perceiving objects moving together as a group (coordinate movement). Law of Pragnanz: the simplest organization, requiring the least cognitive effort, will emerge as the figure. Sensation and perception67
  68. 68. Sensation and perception68  Perceptual Constancy: perceiving the environment as remaining the same even in spite of changes in sensory input  Four best-known constancies:  Size  Shape  Color  Brightness B. Perceptual Constancies
  69. 69. Size constancy Sensation and perception69
  70. 70. Shape constancy: the same perception in spite of the image on the retina. Sensation and perception70
  71. 71.  Different shapes but the same perception Sensation and perception71
  72. 72. Brightness constancy Sensation and perception72
  73. 73. Color constancy  Believe it or not both square “A” and “B” have the same color.  Relative luminance ( the amount of light an object reflects related to its surrounding) determines perceived brightness Sensation and perception73
  74. 74. Sensation and perception74
  75. 75.  These three blue colors are the same but they are influenced by the context. Sensation and perception75
  76. 76. Can you label these examples of size, shape, color, & brightness constancies? Sensation and perception76
  77. 77. Perceptual organization for other senses  Perceptual organization can go beyond vision it can be also applicable to assembling sounds, etc. for a better understanding. Sensation and perception77
  78. 78. Sensation and perception78  Depth Perception: ability to perceive three dimensional space and judge distance  It involves binocular and monocular cues C. Depth Perception
  79. 79. Visual cliff —infants hesitate to crawl over the glass, demonstrating some depth perception Sensation and perception79
  80. 80. Sensation and perception80 Binocular cues Binocular cues: using information from both eyes for depth perception. Our eyes are about 2.5 inches apart and they receive different pictures Binocular depth cues involve: –Retinal Disparity: separation of the eyes causes different images to fall on each retina especially for near objects) –Convergence: when the eyes inward to point toward a nearby object) – stereoscopic vision: occurs when both images are merged into one,
  81. 81. Sensation and perception81 Retinal disparity (left) & Convergence (right)
  82. 82. Monocular cues  Monocular cues help us to estimate depth and distance of 2D objects. They include: Sensation and perception82
  83. 83. Sensation and perception83 1. Linear perspective 2. Interposition 3. Relative size 4. Texture gradient 5. Aerial perspective 6. Light & shadow 7. Relative height
  84. 84.  Interposition: One object blocks another  Linear perspective: Parallel lines converge in the distance  Texture gradient: Texture of distant objects appears to be finer rather than coarser  Shading: 3D objects cast shadows  Aerial Perspective: Far objects are fuzzy  Familiar size: Familiar objects that appear small are inferred to be distant  Relative size: When looking at 2 objects of known similar size, the smaller is seen as further away  Texture gradient: the coarseness decreases as we move away Sensation and perception84
  85. 85.  Relative Size: objects of similar size, we perceive the one that casts a smaller retinal image to be farther away. Sensation and perception85
  86. 86.  Interposition/occlusion: objects that occlude (block) other objects tend to be perceived as closer. Sensation and perception86
  87. 87.  Shadow: shadow and light will help in 3D perception Sensation and perception87
  88. 88.  Motion parallax: when far objects appear to move forward and near objects backward Sensation and perception88
  89. 89.  Linear perspective: parallel lines appear to converge as we move farther Sensation and perception89
  90. 90. D. Motion perception  The vestibular system works to keep the visual system informed of the movements of your head.  We see motion when an object is moving relative to the background.  Local movement: when certain objects move and others remain stationary  Global movement: when a person moves and everything in the visual field moves Sensation and perception90
  91. 91. Movement illusions  Stroboscopic movement: is an illusion of movement created by a rapid succession of stationary images.  Induced movement: the movement of other object induces the perception of movement in another  Waterfall illusion: apparent movement of a flowing stream  The phi phenomena: illusion of movant occurring when adjacent lights are turned on and off alternatively. This is exploited by many a nightclub and motel owner  Motion after effect: perception of movement after the motion is already over Sensation and perception91
  92. 92. Interpretation Sensation and perception92  Interpretation (how the brain explains sensations) involves three major factors: 1. Perceptual Adaptation: brain adapts to changed environments 2. Perceptual Set: readiness to perceive in a particular manner, based on expectations 3. Frame of Reference: based on the context of the situation
  93. 93. 2.3.5. Illusions Sensation and perception93 Illusion: false or misleading perception that helps scientists study the processes of perception
  94. 94. Types of illusions  Distortions (or geometric illusions): when we misperceive the stimuli  Ambiguous (or reversible) figures: figures having two or more plausible interpretations  Paradoxical figures (or impossible objects): paradoxical figures look ordinary enough at first, on closer inspection we realise they cannot exist in reality (hence ‘paradoxical’).  Fictions: figures that create perceptions of non- existing things Sensation and perception94
  95. 95. Illusions of Distortions The Muller-Lyer Illusion Which vertical line is longer? Sensation and perception95
  96. 96.  The horizontal-vertical illusion Which line is longer? Sensation and perception96
  97. 97. Pönzo illusion Sensation and perception97
  98. 98. Sensation and perception98
  99. 99. Sensation and perception99
  100. 100. The spiral circle illusion Sensation and perception100
  101. 101. The Hermann grid: Is there a black dot in the middle Sensation and perception101
  102. 102. Sensation and perception102 Ames Room Illusion
  103. 103. Sensation and perception103 Do you notice anything wrong with these photos of actress Julia Roberts?
  104. 104. Sensation and perception104  Now that the photos are inverted, can you explain how this is an example of perceptual set?
  105. 105. Ambiguous figures  Sensation and perception105
  106. 106. What do you see inside the bottle? How many dolphins do you see? Sensation and perception106
  107. 107. Sensation and perception107
  108. 108. Fictitious illusions  The white triangle is false  The line is fictitious Sensation and perception108
  109. 109. Paradoxical figures Sensation and perception109
  110. 110. Sensation and perception110
  111. 111. Other perceptual deficiencies  Change blindness: People fail to recognize changes occurring in a visual field  Inattention blindness: failure to attend some details of stimuli esp. unexpected  Repetion blindness: failure to detect repeated stimulus  Look at at the following (most people don’t realize that “at” is repeated. Sensation and perception111
  112. 112. 2.4. Extrasensory Perception (ESP)  Extrasensory Perception (ESP): supposed “psychic” abilities that go beyond the known senses. Telepathy: mind to mind communication  Clairvoyance: seeing without the eye  Precognition: perceiving things/events before they happen  Psychokinesis (pk): moving things without touching them • ESP research is criticized for its lack of experimental control & replicability. Sensation and perception112
  113. 113.  “A person who talks a lot is sometimes right”. Spanish proveb Sensation and perception113
  114. 114. Before conclusion  If you assume your senses give you an accurate and undistorted picture of the world, you are probably wrong. If you don’t believe me, try this.  Silently read the backwards statement below. Flip if over in your mind. What does it say?  .rat eht saw tac ehT Sensation and perception114
  115. 115. Answer  How many people saw this: The cat saw the rat.  Look at it again: .rat eht saw tac ehT  How many people saw this: The cat was the rat.  Answer: The cat was the tar. Sensation and perception115
  116. 116. To conclude  Perception depends up on:  Biological factors  Physical factors  Cultural factors  Psychological factors Sensation and perception116 To East African, the woman sitting is balancing a metal box on her head, while the family is sitting under a tree.