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SENSATION AND PERCEPTIONModules 16 & 17
PERCEPTUAL ORGANIZATION
3
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.
4
Organization of the visual field into objects (figures) that stand out from their
surroundings (ground).
FORM PERCEPTION
Tim
e Savings S
uggestion, © 2003 R
oger Sheperd.
5
GROUPING
After distinguishing the figure from the ground, our perception needs to organize the figure into a meaningful form using
grouping rules.
SIMILARITY
PROXIMITY
CONTINUITY
Our tendency to see patterns and therefore perceive things as belonging together if they form some type of continuous pattern.
CLOSURE
10
GROUPING & REALITY
Although grouping principles usually help us construct reality, they may occasionally lead us
astray.
Both photos by W
alter Wick. R
eprinted from G
AM
ES
Magazine. .©
1983 PCS G
ames L
imited Partnership
11
DEPTH PERCEPTION
Visual Cliff
Depth perception enables us to judge distances. Gibson and Walk (1960)
suggested that human infants (crawling age) have depth perception. Even newborn
animals show depth perception.
Inne
rvis
ions
Visual Cliff Video
PERCEIVING DISTANCE
Monocular Cues those cues which can
be seen using only one eye.
They include: Relative size Interposition Relative clarity Texture gradient Relative height Relative motion Linear perspective Light and shadow
Binocular Cues those depth cues in
which both eyes are needed to perceive.
There are two important binocular cues:
Convergence Retinal disparity.
BINOCULAR CUE: CONVERGENCE
The fact that the closer an object, the more inward our eyes need to turn in order to focus. The farther our eyes converge, the closer an object appears to be.
CONVERGENCE VS. ACCOMMODATION
Convergence- Eyes move toward or away from each other Accommodation- Lens moves to bring the vision into focus
Good up to 20 feet
BINOCULAR CUE: RETINAL DISPARITY
The 2.4 inch (6 cm) distance between the two pupils causes us to see two slightly different images of the world. This displacement between the horizontal positions of corresponding images is called binocular disparity.
Our eyes see two images which are then sent to our brains for interpretation, the distance between these two images, or their retinal disparity, provides another cue regarding the distance of the object. Gives us stereoscopic vision
17
BINOCULAR CUE
Retinal disparity: Images from the two eyes differ. Try looking at your two index fingers when
pointing them towards each other half an inch apart and about 5 inches directly in front of your eyes. You will see a “finger sausage” as shown in
the inset.
18
MONOCULAR CUES
Relative Size: If two objects are similar in size, we perceive the one that casts a
smaller retinal image to be farther away.
19
MONOCULAR CUES
Interposition: Objects that occlude (block) other objects tend to be perceived as closer.
Rene M
agritte, The Blank Signature, oil on canvas,
National G
allery of Art, W
ashington. Collection of
Mr. and M
rs. Paul Mellon. Photo by R
ichard Carafelli.
OVERLAP-INTERPOSITION-SUPERPOSITION-OCCLUSION
those objects covering part of another object is perceived as closer.
CLARITY-AERIAL-ATMOSPHERIC PERSPECTIVE
Similar to texture, objects tend to get blurry as they get farther away, therefore, clearer or more crisp images tend to be perceived as closer.
TEXTURE GRADIENT Objects tend to become
smoother as the object gets farther away, suggesting that more detailed textured objects are closer.
23
MONOCULAR CUES
Relative Height: We perceive objects that are higher in our field of vision to be farther away than
those that are lower.
Image courtesy of S
haun P. Vecera, P
h. D.,
adapted from stim
uli that appered in Vecrera et al., 2002
24
MONOCULAR CUES
Relative motion: Objects closer to a fixation point move faster and in opposing direction to those objects that are farther away from a fixation point, moving slower and in the
same direction.
25
MONOCULAR CUES
Linear Perspective: Parallel lines, such as railroad tracks, appear to converge in the distance. The more the lines converge, the
greater their perceived distance.
© T
he New
Yorker C
ollection, 2002, Jack Ziegler
from cartoonbank.com
. All rights reserved.
26
MONOCULAR CUES
Light and Shadow: Nearby objects reflect more light into our eyes than more distant objects. Given two identical objects, the dimmer one appears to
be farther away.
From
“Perceiving S
hape From
Shading” by V
ilayaur S
. Ram
achandran. © 1988 by S
cientific Am
erican, Inc. A
ll rights reserved.
27
PERCEPTUAL CONSTANCY
Perceiving objects as unchanging even as illumination and retinal
images change.
28
Perceiving familiar objects as having consistent color even when changing
illumination filters the light reflected by the object.
COLOR CONSTANCY
Color Constancy
29
SIZE-DISTANCE RELATIONSHIP
The distant monster (below, left) and the top red bar (below, right) appear bigger
because of distance cues.
From Shepard, 1990
Alan C
hoisnet/ The Im
age Bank
30
SIZE-DISTANCE RELATIONSHIP
Both girls in the room are of similar height. However, we perceive them to be of different heights as they stand in the
two corners of the room.
Both photos from S. Schwartzenberg/ The Exploratorium
31
AMES ROOM
The Ames room is designed to demonstrate the size-distance illusion.
32
LIGHTNESS CONSTANCY
The color and brightness of square A and B are the same.
Courte
sy E
dwar
d Ade
lson
PERCEPTUAL INTERPRETATION
34
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 ourperceptual interpretation?
35
SENSORY DEPRIVATION & RESTORED VISION
After cataract surgery, blind adults were able to regain
sight. These individuals could
differentiate figure and ground
relationships, yet they had difficulty distinguishing a
circle and a triangle (Von Senden,
1932).
36
FACIAL RECOGNITION
After blind adults regained sight, they
were able to recognize distinct features, but
were unable to recognize faces.
Normal observers also show difficulty in facial recognition when the
lower half of the pictures are changed.
Courtesy of R
ichard LeG
rand
37
Kittens raised without exposure to horizontal lines later had difficulty
perceiving horizontal bars.
Blakemore & Cooper (1970)
SENSORY DEPRIVATION
38
PERCEPTUAL ADAPTATION
Visual ability to adjust to an
artificially displaced visual field, e.g., prism glasses.
Courtesy of H
ubert Dolezal
39
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.
40
(a) Loch ness monster or a tree trunk; (b) Flying
saucers or clouds?
PERCEPTUAL SET
Other examples of perceptual set.
Frank Searle, photo Adam
s/ Corbis-Sygm
a
Dick R
uhl
41
Is the “magician cabinet” on the floor or hanging from the ceiling?
CONTEXT EFFECTS
Context can radically alter perception.
42
To an East African, the woman sitting is balancing a metal box on her head, while the family is sitting
under a tree.
CULTURAL CONTEXT
Context instilled by culture also alters perception.
43
PERCEPTION REVISITED
Is perception innate or acquired?
EXTRASENSORY PERCEPTION
45
IS THERE EXTRASENSORY PERCEPTION?
Perception without sensory input is called extrasensory perception (ESP). A large
percentage of scientists do not believe in ESP.
46
CLAIMS OF ESP
1. Telepathy: Mind-to-mind communication. One person sending thoughts and the other receiving them.
2. Clairvoyance: Perception of remote events, such as sensing a friend’s house on fire.
3. Precognition: Perceiving future events, such as a political leader’s death.