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Sensation and Perception

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									Perception and Illusion




           Module Nine
Learning Objectives

   How does sensation differ from perception?

   What are the processes involved in depth
    perception?

   Why are we tricked by visual illusions?
Difference between sensation and
perception

   Sensation
    –   The stimulation of the sense receptors
   Perception
    –   The organization and interpretation of sensory stimulation
    –   Despite an inverted retinal image, we don’t perceive flipped
        images
    –   Behavior affected by experience and learning
    –   People’s expectations influence what they see
   Gestalt psychology
    –   The whole (perception) is greater than the sum of its parts
        (sensation)
Gestalt Principles of Grouping

   Proximity
    –   Seeing rows rather than
        columns
    –   We perceive things that are
        close to be a single unit
   Continuity
    –   Seeing lines that connect 1
        to 2 and 3 to 4 in C
    –   Viewers tend to see
        elements in ways that
        produce smooth
        continuation
Gestalt Principles of Grouping


   Similarity
    –   Seeing columns of
        orange and red dots
    –   Objects sharing features
        are grouped together
   Closure
    –   Seeing a horse in D
    –   Viewers tend to supply
        missing elements to
        close figure
Closure
Context Effects


   How we see the middle
    character, depends on
    whether we examine
    the rows or the columns
Context Effects


   How we perceive color
    is dependent upon
    nearby colors.
   The pinks are the same
    shade
   Op art from the 70s
    capitalized on this and
    other perceptual
    illusions
Depth and Distance Perception

   Binocular cues depend on input from both
    eyes
    –   Retinal disparity
            Each eye has a slightly different view
            decreases with distance
    –   Convergence
            eyes moving closer together as object draws near
Depth and Distance Perception

   Monocular cues depend on input from only one eye
    – Relative image size (smaller objects are father
      away)
    – Pictorial depth cues (linear perspective)
    – Interposition
           Closer objects will block view of more distant objects
Muller-Lyer Illusion
Muller-Lyer Illusion
Ponzo Illusion

   The retinal images of
    the red lines are equal!
   Depth cues trick us into
    perceiving the upper
    line as more distant
   Because of size
    constancy, an object
    that is farther away but
    casts same retinal
    image must be larger
Optical illusions

   Show how perceptual organization can fool
    us
   We use perceptual hypotheses to organize
    our sensory experiences
   Sometimes, as is the case in optical illusions,
    our hypotheses our wrong

								
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