Perceptual Organization  Illusions  Gestalt organization  Depth perception  Binocular cues of vision (2)  Monocular cues of vision (8)  Feature extraction

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  • Slide 1
  • Perceptual Organization Illusions Gestalt organization Depth perception Binocular cues of vision (2) Monocular cues of vision (8) Feature extraction Motion perception Constancy
  • Slide 2
  • Perceptual Organization When vision competes with other senses vision usually wins a phenomenon called visual capture. How do we form meaningful perceptions from sensory information? We organize it. Gestalt psychologists showed that a figure forms a whole different than its surroundings.
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  • Perceptual Illusions To understand how perception is organized, illusions provide good examples. It is as good to study faulty perception as other perceptual phenomena. The Muller-Lyer illusion Line AB is longer than line BC.
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  • More Muller-Lyer illusions
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  • Poggendorf Illusion involves the misperception of the position of one segment of a transverse line that has been interrupted by the contour of an intervening structure (here a rectangle) acute angles in the figure are seen by viewers as expanded though the illusion diminishes or disappears when the transverse line is horizontal or vertical.
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  • Tall Arch Vertical dimension of the arch looks longer than the horizontal dimension when both are equal. Rick Friedman/ Black Star
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  • Illusion of a Worm Figure on the right gives us the illusion of a blue hazy worm when it is nothing else but blue lines identical to the picture on the left. 1981, by permission of Christoph Redies and Lothar Spillmann and Pion Limited, London
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  • 3-D Illusion To perceive this figure in two dimensions takes a great deal of effort. Reprinted with kind permission of Elsevier Science-NL. Adapted from Hoffman, D. & Richards, W. Parts of recognition. Cognition, 63, 29-78
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  • Organization of the visual field into objects (figures) that stand out from their surroundings (ground). Form Perception This is a figure-ground relationship
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  • M.C. Escher--Night & Day
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  • Grouping according to Gestalt Having discriminated figure from ground our perception needs to organize figure into meaningful form using grouping rules.
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  • Grouping & Reality Usually grouping principles help us construct reality but at times lead us astray. Both photos by Walter Wick. Reprinted from GAMES Magazine.. 1983 PCS Games Limited Partnership
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  • Depth Perception Visual Cliff Experiment-Eleanor Gibson Depth perception enables us to judge distances. Gibson and Walk (1960) suggested that human infants (crawling age) have depth perception. Even new born animals show depth perception. Innervisions
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  • Binocular Cues (need both eyes working together) Convergence: Neuromuscular cues. Your eyes move together the closer the object is to your face and move away from one another as the objects moves away from your face.
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  • Binocular Cues Retinal disparity: Images from the two eyes differ because of the space between them. Try looking at your two fingers half an inch apart about 5 inches away. You will see a finger sausage as shown in the inset. The closer the object is to our eyes, the greater the difference between the images we perceive.
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  • Monocular Cues Relative Size: If two objects are similar in size, we perceive one that casts a smaller retinal image as farther away.
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  • Monocular Cues Interposition: Objects that occlude (block) other objects tend to be perceived as closer. Rene Magritte, The Blank Signature, oil on canvas, National Gallery of Art, Washington. Collection of Mr. and Mrs. Paul Mellon. Photo by Richard Carafelli.
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  • Monocular Cues Relative Clarity: Because light from distant objects passes through more air, we perceive hazy objects as farther away than sharp clear objects.
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  • Monocular Cues Texture Gradient: Indistinct (fine) texture signals increasing distance. Eric Lessing/ Art Resource, NY
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  • Monocular Cues Relative Height: We perceive objects higher in our field of vision as farther away. This can create the horizontal- vertical illusion if viewed with both eyes and can be reduced by closing one eye.
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  • Monocular Cues Relative motion: Objects closer to a fixation point move faster and in opposing direction to objects farther away from a fixation point, which move slower and in the same direction.
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  • Monocular Cues Linear Perspective: Parallel lines like rail road tracks, appear to converge with distance. The more the lines converge, the greater their perceived distance. This is the Ponzo Illusion
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  • Monocular Cues Light and Shadow: Nearby objects reflect more light to our eyes. Given two identical objects, the dimmer one seems further away. From Perceiving Shape From Shading by Vilayaur S. Ramachandran. 1988 by Scientific American, Inc. All rights reserved.
  • Slide 28
  • Feature Extraction The identification and analysis of specific elements of a sensory input. Allows for encoding of new info into memory 2 benefits Helps you identify it Helps compare it to other inputs Depends to some degree on knowing what to look for Motion capture---remember the motion dots in the video (dancing/basketball/fencing???)--link(dancing/basketball/fencing???) 4 Steps: Detection Pattern dissection Feature comparison in memory Recognition
  • Slide 29
  • Motion Perception Motion Perception: Objects that tend to travel towards us grow in size and ones that move away shrink in size. The same is true when the observer moves to or from an object.
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  • Apparent Motion Phi PhenomenonPhi Phenomenon: When lights flash at certain speed they tend to present illusions of motion. Neon signs and Christmas chaser lights use this principle to create motion perception.( lilac chaser link) Stroboscopic EffectStroboscopic Effect: It occurs when the view of a moving object is represented by a series of short samples as distinct from a continuous view (like a flip book) or a wagon wheel spinning(wagon wheel link), (helicopter link)wagon wheel link)(helicopter link) Two lights flashing one after the other. One light jumping from one point to another: Illusion of motion.
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  • Perceptual Constancy Perceiving objects as unchanging even as illumination and retinal image change. Perceptual constancies include constancies of shape and size. Shape Constancy
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  • Size Constancy Stable size perception amid changing size of the stimuli. Size Constancy
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  • Size-Distance Relationship The distant monster and the top red bar appear bigger because of distance cues. From Shepard, 1990 Alan Choisnet/ The Image Bank
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  • Horizon Moon
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  • High moon on a clear night.
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  • Size-Distance Relationship Both girls in the room are of similar height, however we perceive them of different heights as they stand in the two corners of the room. Both photos from S. Schwartzenberg/ The Exploratorium
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  • Ames Room An Ames room is designed to give size-distance illusion.
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  • Lightness Constancy The color and brightness of square A and B are the same. Courtesy Edward Adelson
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  • Perceiving familiar objects as having consistent color, even if changing illumination filters the light reflected by the object. Color Constancy
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  • Optical illusions you should know Afterimage effect Ames Room Checker-shadow Figure-ground Moon illusion Muller-Lyer Necker cube Phi phenomenon Ponzo illusion Vertical-horizontal (tall arch)
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  • AP info Why do we see illusions? There are 2 binocular cues (you need both eyes)convergence and retinal disparity There are 8 monocular cues (one eye) interposition, linear perspective, texture gradient, relative size, height, motion, clarity, light/shadow
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  • Perceptual Interpretation Perceptual sets and schemas Context effects ESP
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  • Perceptual Interpretation Immanuel Kant (1724-1804) maintained that knowledge comes from our inborn ways of organizing sensory experiences (NATURE). John Locke (1632-1704) argued that through our experiences we also learn to perceive the world (NURTURE). How important is experience in shaping our perceptual interpretation?
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  • Top-Down Processing We perceive by filling the gaps in what we sense. I _ant ch_co_ate ic_ cr_am. Based on our experiences and schemas. If you see many old men in glasses, you are more apt to process a picture of an old man (even when you may be in error).
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  • Restored Vision After cataract surgery blind adults were able to regain sight. These individuals could differentiate