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Basic Perceptual Processes

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					Chapter 3


  Basics of Perception
    and Awareness
            Sensation and Perception
                Basic Principles

• Sensation: A process by which our sensory
  receptors and nervous system receive and
  represent stimulus energy.
• Perception: A process of organizing and
  interpreting sensory information, enabling us to
  recognize meaningful objects and events.
• The connection between sensation and
  perception is not 1 to 1, things are added and
  subtracted.
               Sensation and Perception
                   Basic Principles

• Bottom-Up Processing: Analysis that begins with the sense
  receptors and works up to the brain’s integration of sensory
  information.
• Top-Down Processing: Information processing guided by
  higher-level mental processes.
   – As when we construct perceptions drawing on our
     experience and expectations.
   – Schema: A mental representation that organizes knowledge
     about related concepts.
 Transduction: Conversion of one form of energy to another.
    In sensation, transforming of stimulus energies into neural
     impulses.
           Basic Issues in Perception
            Constructed or Direct?

• Constructive View
  – Perceptions are “built” (i.e., constructed)
  – Mix of stimulus info, expectations, knowledge
  – Empiricist’s view
• Direct View
  – Perceptions are based on uninterpreted
    information
  – Taken directly from environment
  – Nativist’s view
            Sensation and Perception
                Basic Principles
             Weber’s Work on Touch

• Two-point Threshold: The smallest distance
  between two points of stimulation at which
  the two points are experienced as two points
  rather than one.
  – He used a compass-like device to
    simultaneously apply pressure to two points on
    the skin.
  – On Touch: Anatomical and Physiological Notes
    (1834) provided charts of the entire body in
    regards to the two-point threshold.
           Sensation and Perception
               Basic Principles
         Weber’s Work on Kinesthesis

• Just Noticeable Difference (jnd): The
  sensation that results if a change in
  stimulus intensity exceeds the differential
  threshold.
           Sensation and Perception
               Basic Principles

 Psychophysics: Study of the relationship
 between the physical characteristics of
 stimuli and our psychological experience
 of them.
   Light: Lumens compared to brightness
   Sound: Decibels compared to loudness
   Temperature: BTU compared to warmth
   Taste: Grams of sugar compared to
    sweetness
            Sensation and Perception
                Basic Principles
             Judgments are Relative

• The jnd is a constant fraction of the
  standard weight.
  – For lifted weights it is about 1/40, for non-
    lifted weights it is about 1/30
• Weber's Law: Just noticeable differences
  correspond to a constant proportion of a
  standard stimulus.
                 Sensation and Perception
                     Basic Principles
                      Weber’s Law

                                    DR
                                       k
                                     R
• R = Reiz, the German word for stimulus, the
  standard stimulus.
 DR = The minimum change in R that could be
  detected.
• k = constant (as seen earlier, k = 1/40 for lifted
  weights)
              Sensation and Perception
                  Basic Principles
                Absolute Threshold

• Absolute Threshold: The smallest amount of
  stimulation that can be detected by an
  organism.
•When stimuli are
detectable less than 50%
of the time (below one’s
absolute threshold) they
are “subliminal”.
                Sensation and Perception
                    Basic Principles
                  Absolute Threshold

• Vision-We can see 1 candle 30 miles away -
  (pretty low threshold!).
• Audition–We can hear a watch tick 20 feet away.
• Taste-We can taste 1 tsp. of sugar in 2 gallons of
  water.
• Smell-We can smell 1 drop of perfume within a 3
  room apartment.
• Touch-We can feel the sensation of a bee wing
  dropped from 1 cm above your back.
                 Sensation and Perception
                      Basic Principles
               The jnd as a Unit of Sensation

• The absolute threshold was useful, but only provided a
  single point of connection between the physical world
  and the psychological world.
• Differential Threshold: The amount that stimulation
  needs to change before a difference in that stimulation
  can be detected.
   – Given a geometric increase in the level of stimulus,
     there will be an arithmetical increase in the level of
     sensation.
• S = k log R
      Sensation and Perception
           Basic Principles
    Estimates of Weber Constants

Electric Shock             Very Small
Pitch                      .003 = 1/333
Deep Pressure              .013 = 1/77
Visual Brightness          .016 = 1/62
Weight                     .050 = 1/20
Loudness                   .088 = 1/11
Smell, Rubber              .104 = 1/10
Cutaneous Pressure         .136 = 1/7
Taste, saltiness           .200 = 1/5
        Sensation
       Light Energy
• Wavelength: The
  distance from the peak
  of one light or sound
  wave to the peak of the
  next.
• Light also exhibits
  properties of particles.
• Intensity: Amount of
  energy in a wave;
  determined by the
  wave’s amplitude.
    Sensation
       Light
(Electromagnetic)
     Energy


  Hue:
  Determined by
  wavelength,
  color we
  experience
Sensation
 The Eye
                    Sensation
                     The Eye


 Accommodation: The process by which the
  eye’s lens changes shape to help focus near or
  far objects on the retina.

 Retina: The light-sensitive inner surface of the
  eye, containing receptor rods and cones plus
  layers of neurons that begin the processing of
  visual information.
                    Sensation
                     The Eye

 Rods: Peripheral retina
  receptors
    Detect black, white and gray
    For peripheral or twilight
     conditions
 Cones: Receptors near center
  of retina
    Fine detail and color vision
    For daylight or well-lit
     conditions
                      Sensation
                       The Eye

 Optic Nerve: Nerve
  that carries neural
  impulses from the
  eye to the brain.
 Blind Spot: Point at
  which the optic nerve
  leaves the eye,
  creating a “blind
  spot” because there
  are no receptor cells
  located there.
Audition- The Ear
                   Sensation
                    Audition
            How Transduction happens
• Hair cells are the nerve cells
  – Changes in the air pressure (the stimulus)
  – affect the fluid in the cochlea
  – the basilar membrane ripples (an undulating wave)
  – wave causes hair cells to bend and
  – trigger neural impulse
  – nerve impulse is sent to thalamus and temporal
    lobe's auditory cortex and we hear.
• TRANSDUCTION IN HEARING IS MECHANICAL -
  FROM VIBRATIONS
               Pattern Recognition


• Pattern Recognition: Step between transduction
  and perception of a stimulus in the environment
  and its categorization as a meaningful object.
  – Identifying an image in sensory memory by drawing
    on past experience or knowledge .
• Agnosia: Patients suffering lesions in certain
  areas of the brain can see objects, but not
  recognize them.
    Pattern Recognition
Visual Information Processing
      Pattern Recognition
  Visual Information Processing

• Feature Detectors:
  Nerve cells in the
  brain that respond
  to specific features
  of the stimulus
     • shape
     • angle
     • movement
                 Pattern Recognition
             Visual Information Processing

• Geons are simple 3-dimensional forms such as spheres,
  cubes, cylinders, cones or wedges. One theory of object
  recognition, Recognition by Components (RBC)
  (Biederman, 1987), proposes that visual input is matched
  against structural representations of objects in the brain.
  These structural representations consist of geons and their
  interrelations (e.g., an ice cream cone could be broken
  down into a sphere located above a cone). Geons can be
  used to represent a large number of possible objects with
  very few components; e.g., 24 geons can be recombined to
  create over 10 million different two-geon objects.
    Pattern Recognition
Visual Information Processing
              Pattern Recognition
          Visual Information Processing

• Parallel Processing: Processing several aspects
 of a problem simultaneously.
  – The brain’s natural mode of information processing
    for many functions, including vision.
                Pattern Recognition
                    Color Vision

• Young-Helmholtz Trichromatic (three color)
  Theory
  – The retina contains three different retinal color
    receptors (cones)-one most sensitive to red, one to
    green, and one to blue-which when stimulated in
    combination can produce the perception of any
    color.
Pattern Recognition
    Color Vision



             • People who
               suffer red-green
               blindness have
               trouble
               perceiving the
               number within
               the design.
               Pattern Recognition
                   Color Vision

• Opponent-Process Theory: Theory that
  opposing visual cortex processes (red-green,
  yellow-blue, white-black) enable color vision.
      • Some cells stimulated by green and
        inhibited by red.
      • Others stimulated by red and inhibited by
        green.
            Pattern Recognition
                Color Vision

• So what is correct?
• Both theories help explain color vision
  – Trichromatic theory explains color vision
    at the retina level.

 – Opponent-process theory explains color
   vision at the brain level.
Pattern Recognition
 Hearing (Audition)
Sound Localization
                 Pattern Recognition
                  Hearing (Audition)
                   Perceiving Pitch
• Place Theory
  – 1st theory of perceived pitch
  – Proposes we hear different pitches because
    different sound waves trigger activity at
    different places along the cochlea's basilar
    membrane.
  – Place theory only explains how we hear high
    pitch sounds.
  – High pitches close to oval window
  – Low pitches at far end of cochlea
               Pattern Recognition
                Hearing (Audition)
                 Perceiving Pitch
• Frequency Theory
  – Suggests we hear different pitches based on
    the frequency of the incoming sound waves
  – e.g.: 100Hz waves = 100 neural
    impulses/second
  – Unfortunately neurons cannot fire faster than
    1000 times per second
  – This theory cannot account for hearing in the
    upper third of a piano key
               Pattern Recognition
                Hearing (Audition)
                 Perceiving Pitch

• Volley principle
  – Suggests that the neural cells can alternate
    firing and achieve a combined frequency
    above 1000 times per second

• Actually, both place and frequency seem to
  influence perceived pitch
                     Perception


• Perception takes over where sensation stops
• Perception is an active and constructive
  process of how we interpret and organize
  sensations
• How the brain interprets and makes sense of
  incoming messages
• There has been a philosophical debate since
  the beginning of philosophy.
 – Empiricists argue for nothing inborn
 – Nativists argue for inborn dispositions
Perceptual Organization



              • Gestalt
                – An organized
                  whole.
                – Tendency to
                  integrate pieces
                  of information
                  into meaningful
                  wholes.
       Perceptual Organization
          Form Perception


Composed of several phenomenon
 – Figure ground
 – Grouping
 – Depth Perception
 – Perceptual constancy
               Perceptual Organization
                  Form Perception
                 Figure and Ground
• Figure and Ground:
  Organization of the visual
  field into objects (figures) that
  stand out from their
  surroundings (ground).
             Perceptual Organization
                Form Perception
                   Grouping
• Grouping: The perceptual tendency to organize
  stimuli into coherent groups.
• Grouping Principles
  – Proximity: group nearby figures together
  – Similarity: group figures that are similar
  – Continuity: perceive continuous patterns
  – Closure: fill in gaps
  – Connectedness: spots, lines and areas are seen as
    unit when connected
         Basic Tasks of Visual Perception
       Perceptual Organizational Processes

• Global Precedence: We tend to notice wholes
before parts.
   – Navon (1977)
      • Presented ambiguous stimuli
      • Had subjects identify local or global letters
      • Subjects were faster at identifying global element
      • Critical interaction: Conflict only interfered with
        identification of local element
      • Findings indicate primacy of noticing global
        features
             Perceptual Organization
                Form Perception
                   Grouping




Proximity            Similarity




Continuity            Closure          Connectedness
                    Perceptual Organization
                       Depth Perception

• Depth Perception
  – Ability to see objects in three dimensions
  – Allows us to judge distance
     Visual Cliff
               Perceptual Organization
                Perceptual Constancy


• We perceive Objects in our world as stable and the
  environment as changing rather than the reverse
• We perceive changes in shape, size, color, or
  brightness as a function of distance, lighting, or
  movement.
  – Size-familiar objects retain their size regardless of
    distance
  – Shape-familiar objects retain shape regardless of
    angle of view
  – Brightness-familiar objects retain their color despite
    differing illumination
Perceptual Organization
 Perceptual Constancy
   Shape Constancy
Perceptual Organization
 Perceptual Constancy
   Color Constancy
Perceptual Organization
 Perceptual Constancy
   Color Constancy
  Perceptual Organization
   Perceptual Constancy
Shape and Size Constancies
  Perceptual Organization
   Perceptual Constancy
Shape and Size Constancies
 Size-Distance Relationship
Perceptual Organization
 Perceptual Constancy
 Lightness Constancy
Perceptual Organization
 Perceptual Constancy
 Lightness Constancy
           Perceptual Interpretation
            Two Conflicting Views



• Immanuel Kant (Nature)
   – Knowledge comes from our inborn ways of
     organizing sensory experiences.
• John Locke (Nurture)
   – Through our experience we also learn to
     perceive the world.
           Perceptual Interpretation
    Sensory Deprivation and Restored Vision


• People born with cataracts can immediately
  sense colors and figure-ground distinctions
  after the cataracts removed, thus supporting
  Kant’s notion of innate perceptions.
• However, these same people could not identify
  by sight those objects which they were familiar
  with by touch, thus supporting Locke’s notion of
  learned perception.
            Perceptual Interpretation
                Perceptual Set
                Context Effects

• We often interpret ambiguous situations based
  on things around it.
• In spoken language, homophones are totally
  ambiguous.
   – The window pane/pain was raised.
      • Standing alone, the word pane/pain is
        indistinguishable
      • In context, it is quite easy to determine
Perceptual Interpretation
    Perceptual Set
    Context Effects
              Perceptual Interpretation
                  Face Perception

• Holistic Processing: Perceiving the whole object.
• Analytic Processing: Perceiving the features which
  comprise the whole.
   – Oliver Sacks wrote a book titled The Man who
     Mistook his Wife for a Hat
      • Included story of a man who mistook his foot for
        a shoe.
• Prosopagnosia: An inability to recognize faces while
  other visual recognition remains unchanged.
• Module: A set of processes that are automatic, fast,
  encapsulated apart from other cognitive systems, and
  located in a localized area of the brain.
    Multi-Sensory Interaction and Integration
                  Synesthesia

• Synesthesia: Input from one sensory modality is
  experienced in another.
   – Strong synesthesia
      • Example: experiencing a smell as “pointy”

  – Weak synesthesia
    • Linguistic in nature
    • Example: Labeling colors as “cool” or
      “warm”
    Multi-Sensory Interaction and Integration
            Comparing the Senses

• Vision tends to dominate the other senses

  – Vision and Audition
     • Ventriloquist Effect: Tendency for visual
       cues to influence localization of sound.

    • McGurk Effect: Visual cues can affect the
      way we hear speech sounds.
     Multi-Sensory Interaction and Integration
             Comparing the Senses
• Vision tends to dominate the other senses
  – Vision and Chemical Senses
      • Visual cues can influence what we smell and
        taste.
  – Vision and Touch
      • Pavani, Spence and Driver (2000) found that
        visual cues can create illusions of touch.
                 Consciousness
           Varieties of Consciousness

• Consciousness refers to our awareness of
  internal and external events.
• Varieties of consciousness
   – Monitoring Consciousness: Reflecting on
     one’s consciousness.
   – Self Consciousness: Knowledge about self.
  – Access Consciousness: Cognitive processes that
    subserve behavior.
  – Phenomenal Consciousness: Subjective
    experience.
                Consciousness
        Dissociations in Consciousness

• Signal detection approach

  – Phenomenal reports of perception don’t
    always match reality.

  – Conscious perception is the product of:
     • Sensitivity (acuteness of perceptual
       processes)
     • Response bias (willingness to report)
                  Consciousness
                Subliminal Perception

• Subliminal Perception
  – Can stimuli below the threshold of conscious
    awareness influence behavior?


• Marcel (1983) gave subjects a Stroop task
  – Responses were influenced by a subliminally
    presented color prime
    • Both inhibitory and excitatory priming found
    • Priming effects small
                Consciousness
              Subliminal Perception

• Cheesman and Merikle distinguish between:
   – Subjective Threshold: Point at which subject
     claims not to have seen prime.
      • Can guess prime at above chance levels.
   – Objective Threshold: Point at which subject
     claims not to have seen prime.
      • Guessing of prime is no better than chance
• Only primes presented below subjective
  threshold produce subliminal priming.
                Visual Attention
               Attentional Capture

• Attentional Capture: A stimulus involuntarily
  captures visual attention.
   – Implicit: Changes some aspect of behavior.
   – Explicit: Leads to a conscious attention
     switch.
                  Visual Attention
                 Attentional Capture

• Inattentional Blindness: Failure to notice obvious
  change in visual scene.
  – Sometimes termed change blindness

  – Simons and Chabris (1999)
     • Subjects watched and attended to a video
     • Over ½ failed to notice bizarre event
                 Auditory Attention


• Auditory attention is limited

• Some conceive of attention as a gateway
  – We must select what receives attention
  – Studied with dichotic listening and speech
    shadowing
  – How do we attend?

				
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