Perception

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Perception

• "Colors, tones, smells, and tastes are mental
  constructions created by the brain out of sensory
  experience. They do not exist, as such, outside
  of the brain. " (Martin, 1991).
• Perception is an active, constructive process
• Al Seckel

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Does perception exist outside of awareness?

• Subliminality
• Selective Attention Focus of conscious awareness
  on a particular stimulus. Cocktail Party
  Phenomenon
• Change and Inattentional Blindness
• djs_lab demos
• Viewable/Downloadable Examples

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Perceptual Organization

• Gestalt Psychology Late 19th/early 20th field
  that emphasized the human tendency to organize
  pieces of information into meaningful patterns or
  wholes (Max Wertheimer, W. Kohler, F. Koffka)
• The brains tendency to organize sensory stimuli
  in order to construct reality helps to explain
  our susceptibility to illusions

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Gestalt Grouping Principles

• The perceptual tendency to organize stimuli into
  coherent groups (Law of Pragnanz or good order).
  We tend to order experience in a manner that is
  regular, orderly, symmetric, and most simple
• proximity--group nearby figures together
• similarity--group figures that are similar
• familiarityfamiliar or meaningful pattern
• continuity--perceive continuous patterns
• closure--fill in gaps
• connectedness--spots, lines, and areas are seen
  as unit when connected
• common fate--when objects move in the same
  direction, we see them as a unit
• Gestalt

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Kanizsas Illusory Triangle

• Illusory and Subjective Contours-Creating images
  where they do not exist

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Perceptual Organization

• Among our most basic perceptual tasks is a type
  of selective attention where we distinguish
  objects as separate from their surroundings, a
  concept known as. . .

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Infamous Rubin
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Which picture predominates for you, the younger
or older woman?
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Reversible figures

• Like with figure ground images in the following
  illustrations the relationship between the
  objects continually reverses.
• Perceptual hypothesis Contends that we bridge the
  gap between whats real and what we see by
  constantly making and testing hypotheses

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The Necker cube
http//dogfeathers.com/java/necker.html
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Binocular cues

• Retinal disparity and stereopisis The brain
  perceives distance and depth by comparing the
  different images received by each eye
• Convergence Eyes come together as objects are
  nearer

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• Stereograms (like 3-D movies) exaggerate retinal
  disparity by placing two slightly separated
  images apart. The brain actively reconstructs
  the images into a 3-D illusion

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Monocular cues

• Interposition/Superposition
• Relative clarity/aerial perspective
• Texture gradient
• Relative height
• Relative size
• Light and shadow
• Linear perspective
• Motion parallax

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Paris Street A Rainy Day Gustave Caillebotte
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Pavement Drawings

• Julian Beever

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Illusions you should know (and their possible
explanations)

• Figure-ground
• Reversible figures (Necker cube)
• Illusory contours (Kanizsa triangle)
• Size-distance illusions (Ames Room, Muller-Lyer
  Ponzo illusion)
• Impossible figures (role of perceptual
  set/schema)
• Think gestaltTop down processing (perceptual
  hypothesis)

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Size-Distance Illusions

• In each of these examples, the top and bottom
  lines are actually the same length.
• In each case the top line looks longer. Because?
• Mueller-Lyer Illusion

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Ames Room

• Monocular depth cues give the illusion that the
  two people are equally far away Ames

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The Ponzo Illusion

• What misassumptions cause this illusion?

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The monocular cues of linear perspective and
relative size are responsible for this illusion.
How? Shepard's Terror Subterra
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More Perception Terms

• Real vs. apparent movement
• Autokinetic effect/illusion
• Stroboscopic motion
• Phi Phenomenon PHI Phenomenon Activity
• Induced movement (stationary-moon)
• Moving Aftereffect (MAE) spiral
  aftereffect/waterfall illusion Motion Aftereffect
• Motion induced blindness (VSR) MIB
• YTMIB

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Motion Illusions

• Freezing Rotation Illusion
• Motion Induced Blindness
• Stepping feet Motion Illusion
• Stereokinetic Phenomenon
• Motion-Bounce Illusion

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Perceptual Constancy

• Perceiving objects as unchanging even as
  illumination and retinal image change
• color
• shape
• size

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Contrast and Color Illusions

• Grid Illusions Hering
• Wertheimer-Koffka-Ring
• Munker-White Illusion
• Adelson -- Checker-shadow illusion
• Lilac Chaser
• Cool Escher-inspired movie An impossible Movie
• Beau Lotto

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The Stroop Effect

• Stroop found that the act of reading could
  interfere with your ability to perform simple
  perceptual distinctions like naming colors
• Stroop Lab Introduction

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Other Misleading Cues and Line Illusions

• Hering Illusion
• Café Wall Illusion

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Impossible Figures
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