Download Gibson and Walk (1960)

Perception
Organizing the Perceptual World – Module 15
General Psych 1
March 8, 2005
Class # 13
Gestalt Psychology
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Based on the assumption that the whole is
greater than the sum of its parts…
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Basic principles:
 Figure-Ground Processing
In a noisy environment, we pick out
features that are important (stands out from
the rest) this is the figure
 The ground is the less relevant stuff
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Figure and Ground
Gestalt Principles of Perceptual Grouping
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Having discriminated figure from ground, we
then try to organize the figure into a meaningful
form
Our minds seem to follow certain rules for
grouping stimuli together
Several rules of perceptual organization
identified by Gestalt psychologists illustrate
their idea that the perceived whole is different
from the mere sum of its parts
Gestalt Principles of Perceptual Grouping
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Proximity
 If figures are near each other we tend to group
them together
Similarity
 If figures are similar to each other we tend to
group them together
Continuity
 We tend to perceive smooth, continuous patterns
rather than discontinuous ones
Closure
 When a familiar figure is interrupted we imagine
the rest of the figure (we finish the picture)
Gestalt Principles of Perceptual Grouping
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Texture
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Simplicity
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When basic stimuli have the same texture people tend to
group them together
People tend to group features of a stimulus in a way that
provides the simplest interpretation of the world
Common Region
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Elements located within some boundary tend to be
grouped together
Gestalt Principles of Perceptual Grouping
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Common Fate
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Sets of objects that are moving in the same
direction and at the same speed are perceived
together (example: marching bands)
Connectedness
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When they are uniformed and linked, we perceive
spots and lines, etc. as a single unit
Depth Perception
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This is our ability to transform two-dimensional
retinal images into three dimensional
perceptions…

Seeing objects in three dimensions enables us to
estimate their distance from us
Nativist-Empiricist Debate
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Nativists (inborn trait) vs. Empiricists (learned trait)

Nativists:
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Mind doesn’t rely on experience for meaning but innately
organizes sensations into perception
Depth perception emerges too early in life to have been
learned
Even adults with limited experience (e.g., handicapped)
experience depth
Empiricists:
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Infants learn depth through feedback from their tactile and
motor experiences
They associate eye movements with hand and arm
movements.
Gibson and Walk (1960)
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These researchers tried to solve this dispute
in their “visual cliff” experiment
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Exp 1: human infants
Gibson and Walk (1960)
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They designed a “visual cliff”, which was actually a
glass-top table
A checkered pattern was positioned close to the glass
under one half of the table (the “shallow” side) and far
below the glass under the other half (the “deep” side)
Infants between the ages of 6 months and 14 months
were placed on the shallow side of the table, and
encouraged to crawl over the edge of the visual cliff on
to the deep side by being offered toys or having their
mothers call them
Most failed to respond to these incentives, suggesting
that they possessed at least some of the elements of
depth perception
Gibson and Walk (1960)

What do you think was the main criticism of
this experiment???
Gibson and Walk (1960)
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Experiment 2:
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Day-old goat
Newly hatched chickens
Again, as with the human infants they
displayed depth perception
But…
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In other studies, new-born chickens are seen
pecking at corn that is in fact ten centimeters
away until they are forcibly removed, no
matter how many times they peck air
Bertenthal & Campos (1978)
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Nine-month-old infants had faster heart rates
than normal when placed on the deep side,
presumably because they were frightened
Held and Hein (1963)
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Experiment 1:
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Kittens raised in darkness until at least six
weeks of age
 They did not retreat from visual cliff
Held and Hein (1963)
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Experiment 2:
 Placed two kittens in the
'kitten carousel' a device
which let one cat move it
while the other followed
around but was not in
control of the motion
 This meant that both cats
had the same visual
experience
 The immobile kittens were
unable to blink and didn't
stretch out their paws when
lowered to the ground
 However, when allowed free
movement they quickly
learned the ability, implying
that the perception of depth
is learned and related to the
motor system
So how are we able to develop depth perception?
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Has to do with the use of certain cues…
 Binocular Cues
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These cues require the use of both eyes
Monocular Cues
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These cues are available to each eye separately
Binocular Cues: The Pencil Tests
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Binocular (Retinal) Disparity
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The difference between the two retinal images of
an object (pencil test #1)
Granrud (1987) – felt that this cue appears to
develop after three months of age thereby
conflicts with Gibson and Walk (1960)
Binocular Cues: The Pencil Tests
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Binocular Convergence
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A muscular cue that indicates the extent to
which our eyes turn inward when we look at
an object (pencil test #2)
Goldstein (1999) – we have basic building
blocks of convergence at birth but with
maturation of our visual systems these further
improve with age
Monocular Cues for Perception of Depth
and Distance
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Interposition
 Depth cue derived from the overlapping position of
objects
Relative Size
 When object gets larger on the retina we assume
they are closer
Textural Gradient
 This is provided by our proximity to an object
Linear Perspective
 Cue provided by the convergence of lines towards
a single point of the horizon
Monocular Cues for Perception of Depth
and Distance
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Motion Parallax
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Accommodation
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Feedback we receive from the muscles in the eye that
causes the lens to bulge or get thinner (pencil test #3)
Haze
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The result of changing positions of an object in space due to
the motion of the object
Aerial perspective acts as a depth cue over long distances
when we are outside
Relative Height
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We perceive objects higher in our field of vision as farther
away (St. Louis Gateway Arch)
Monocular Cues for Perception of Depth
and Distance
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Light
 Nearby objects reflect more light in our eyes therefore
given two identical objects, the dimmer one seems
farther away
Shadow
 This also produces a sense of depth consistent with
the assumed light source
Perception of Motion
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Looming
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The rapid expansion of the size of an image so that
it fills the retina
 If this expansion is equal in all directions then its
coming right at you – if its more to one side it will
miss you
 Sports Psych – could it be that “expert catchers”
unconsciously are able to detect these angles
better?
Perception of Motion
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Stroboscopic Motion (phi phenomenon)
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Occurs because of our tendency to interpret as
continuous as series of still images flashed in
succession
 Videotapes show 30 per second – memory of one
is long enough so that we don’t notice any gaps
Perceptual Constancies
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Size Constancy
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A nearer object will have a larger retinal image
but we don't interpret the object as being larger
Without size constancy people would appear to
grow as they walked towards you and shrink as
they walk away
Our visual system appears to estimate distance
and size together
Perceptual Constancies
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Shape Constancy
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Objects viewed from different orientations have
different forms but we don't interpret them as
different objects
Experience is important determining shape
constancies
Lightness Constancy
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No matter how the amount of light striking an
object changes, the object’s perceived
brightness does not change
Optical Illusions
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A misinterpretation of a visual stimulus…
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When the "real" and the perceived do not match
Illusions mislead us by playing on the ways we
organize and interpret our sensations
“Visual-capture” phenomenon
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When there is a conflict between visual and other
sensory information, vision seems to dominate or
capture the other senses
 Examples:
 When the sound of a movie comes from the
projector behind us, we still perceive it as coming
from the screen (we “see” the actors talking)
 Same as we perceive the voice from the
ventriloquist's dummy
Optical Illusions
Which Line Is Longer?
A-C on the Left or A-B on the Right?