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.
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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
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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
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 figure and
ground relationship however had difficulty discriminating a circle
and a triangle (Von Senden, 1932).
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Facial Recognition After blind adults were able to regain sight
they were unable to recognize faces, they would only recognize
distinct features. Normal observers also show difficulty in facial
recognition when lower half of the pictures are changed. Courtesy
of Richard LeGrand
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Perceptual Set A mental predisposition to perceive one thing
and not another. What you see in the center picture is influenced
by flanking pictures. From Shepard, 1990.
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Perceptual set and Auditory perception 1970s and 1980s several
groups accused recording artists of inserting satanic messages
within songs. The message could be heard if the track was played
backward (backmasking) This is different than phonetic reversal Ask
yourself how does your expectancy affect what you perceivehere are
some examples
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(a) Loch ness monster or a tree trunk; (b) Flying Saucers or
Clouds? Perceptual Set Other examples of perceptual set. Frank
Searle, photo Adams/ Corbis-Sygma Dick Ruhl
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Children's schemas represent reality as well as their abilities
to represent what they see. Schemas Schemas are concepts that
organize and interpret unfamiliar information. Courtesy of Anna
Elizabeth Voskuil
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Eye & Mouth Eyes and mouth play a dominant role in face
recognition. Courtesy of Christopher Tyler
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Is the magician cabinet on the floor or hanging from the
ceiling? Context Effects Context can radically alter
perception.
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To an East African the sitting woman is balancing a metal box
on her head and the family was sitting under a tree. Cultural
Context Context instilled by culture also alter perception.
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Perception Revisited Is perception innate or acquired?
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Perception & Human Factors Human factors psychologists
design machines that assist our natural perceptions. The knobs for
the stove burners on the right is easier to understand than one on
the left. Photodisc/ Punchstock Courtesy of General Electric
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Is There Extrasensory Perception? Perception without sensory
input is called extrasensory perception (ESP). A large percentage
of scientists do not believe in ESP. But.
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Claims of ESP 1.Telepathy: Mind-to mind communication. One
person sending thoughts and the other receiving it. 2.Clairvoyance:
Perception of remote events. Like sensing a friends house on fire.
3.Precognition: Perceiving future events. Such as a political
leaders death. 4.Psychokinesis: The ability to control movement of
inanimate objects (Ex. Yuri Geller)
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Devils Tuning Fork
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M. C. Escher: Relativity
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M. C. Escher: Waterfall
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AP info Gestalt and wanting the whole picture What role do
schemas play in perception? Expectancy set and perceptual set
Experiences Schemas