Sensation and Perception Chapter 6. Sensation 3 The Eye.
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Sensation and Perception
Chapter 6
Sensation
3
The Eye
4
Photoreceptors
E.R. Lewis, Y.Y. Zeevi, F.S Werblin, 1969
Perception
6
Test your Blind Spot
Use your textbook. Close your left eye, and fixate your right eye on the black dot. Move the page towards your eye and away from
your eye. At some point the car on the right will disappear due to a blind spot.
7
Bottom-up Processing
Analysis of the stimulus begins with the sense receptors and works up to the level of
the brain and mind.
Letter “A” is really a black blotch broken down into features by the brain that we perceive as an
“A.”
8
Feature Detection
Nerve cells in the visual cortex respond to specific features, such as edges, angles,
and movement.
Ros
s K
inna
ird/
Alls
port
/ Get
ty I
mag
es
9
Visual Information Processing
parallel processing The brain divides a visual scene into subdivisions such as color,
depth, form, movement, etc.
10
Top-Down Processing
Information processing guided by higher-level mental processes as we construct perceptions, drawing on our experience
and expectations.
THE CHT
11
Thresholds
Absolute Threshold: Minimum stimulation needed to detect a particular stimulus 50%
of the time.
Pro
port
ion
of
“Yes”
Resp
on
ses
0.0
0
0
.50
1.0
0
0 5 10 15 20 25 Stimulus Intensity (lumens)
12
Subconscious Sense and Perception
Subliminal Threshold: PrimingLength of effects
Adaptation/Habituation
• Stare at the image, don’t move your eyes around
15
Perceptual Organization
Flipped image
17
Figure/GroundT
ime S
avings Suggestion, ©
2003 Roger S
heperd.
18
Grouping
19
Depth Perception
Visual Cliff
Inne
rvis
ions
20
Binocular Cues
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.
21
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.
22
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.
23
Monocular Cues
Relative motion:
24
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.
25
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.
26
Perceptual Constancy
Perceiving objects as unchanging even as illumination and retinal
images change.
27
Color Constancy
Color Constancy
28
Lightness Constancy
The color and brightness of square A and B are the same.
Courte
sy E
dwar
d Ade
lson
29
Size-Distance Relationship
From Shepard, 1990
Alan C
hoisnet/ The Im
age Bank
30
Size-Distance RelationshipBoth 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
Perceptual Interpretation
How important is experience in shaping ourperceptual interpretation?
33
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
34
Kittens raised without exposure to horizontal lines later had difficulty
perceiving horizontal bars.
Blakemore & Cooper (1970)
Sensory Deprivation
Top down emotional effects
• Music• Fatigue• Carrying heavy versus light objects• Previous performance
36
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.
37
Taste
Sweet Sour Salty Bitter Umami(FreshChicken)
Gustation/Taste – a close-up view of the tongue
Why does some food taste “hot”?
• Hot chili peppers are sensed by pain fibers in the tongue, which are activated by capsaicin
• Was evolved in the peppers to prevent them from being eaten
40
Smell
What is your favorite scent?
42
Smell and Memories
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