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Perception
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Perception
The process of selecting, organizing, and
interpreting sensory information, which enables us
to recognize meaningful objects and events.
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Selective Attention
Perceptions about objects change from moment to moment.
We can only focus on limited aspects of sensory input at
any given time
e.g. : “Cocktail Party Effect”
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Perceptual Illusions
Illusions provide good examples in
understanding how perception is organized.
Studying faulty perception is as important as
studying other perceptual phenomena.
Line AB is longer than line BC.
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Tall Arch
Rick Friedman/ Black Star
In this picture, the
vertical dimension
of the arch looks
longer than the
horizontal
dimension.
However, both are
equal.
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Perceptual Organization
How do we form meaningful perceptions
from sensory information?
We organize it. Gestalt psychologists
showed that a figure formed a “whole”
different than its surroundings.
called a “gestalt”
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Form Perception
Organization of the visual field into objects
(figures) that stand out from their surroundings
(ground).
Time Savings Suggestion, © 2003 Roger Sheperd.
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Grouping
After distinguishing the figure from the ground,
our perception needs to organize the figure into
a meaningful form using grouping rules.
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Perception in Brain

Our perceptions are a combination of
sensory (bottom-up) and cognitive (topdown) processes.
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Perceptual Interpretation
Immanuel Kant (1724-1804) maintained that
knowledge comes from our inborn ways of
organizing sensory experiences.
John Locke (1632-1704) argued that we learn to
perceive the world through our experiences.
How important is experience in shaping our
perceptual interpretation?
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Sensory Deprivation
Kittens raised
without exposure to
horizontal lines later
had difficulty
perceiving horizontal
bars.
Blakemore & Cooper (1970)
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Perceptual Set
Other examples of perceptual set.
Dick Ruhl
Frank Searle, photo Adams/ Corbis-Sygma
(a) Loch ness monster or a tree trunk;
(b) Flying saucers or clouds?
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Cultural Context
Context instilled by culture also alters
perception.
To an East African, the woman sitting is balancing a metal
box on her head, while the family is sitting under a tree.
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Perception Revisited
Is perception innate or acquired?
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Human Factors & Misperceptions
Understanding human factors enables us to
design equipment to prevent disasters.
Two-thirds of airline crashes caused by human error are
largely due to errors of perception.
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