Transcript EXPLORING PSYCHOLOGY (7th Edition in Modules) David Myers

Introduction to Sensation
and Perception: Vision
Module 11
1
Sensation Overview
Sensing the World:
Some Basic Principles
 Thresholds
 Sensory Adaptation
Vision
 The Stimulus Input: Light Energy
 The Eye
 Visual Information Processing
 Color Vision
2
Sensation
 Sensation
 a process by which our sensory
receptors and nervous system receive
and represent stimulus energy
 Perception
 a process of organizing and interpreting
sensory information, enabling us to
recognize meaningful objects and
events
3
4
5
Figure 5.14: Categorizing Perceptions:
What Do You See Here?
Illustration from Sensation and Perception, Fourth Edition, by Stanley Coren, Lawrence
M. Ward, and James T. Enns, copyright © 1994 by Harcourt, Brace, and Company,
reprinted by permission of the publisher.
6
Figure 5.19: Another Version of
Figure 5.14
From Sensation and Perception, Fourth Edition by Stanley Coren, Lawrence M. Ward, and James T. Enns, p. 393; Copyright c 1994. Reprinted with
permission of John Wiley & Sons, Inc.
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 Analysis – Bottom-Up
9
Top-Down Processing
Information processing guided by higher-level
mental processes as we construct perceptions,
drawing on our experience and expectations.
THE CHT
10
Top down example
Aoccdrnig to rscheearch at Cmabrigde
Uinervtisy, it deosn’t mttaer in waht oredr the
ltteers in a wrod are, the olny iprmoetnt tihng
is taht the frist and lsat ltteer be at the rghit
pclae. The rset can be a total mses and you
can sitll raed it wouthit a porbelm. Tihs is
bcuseae the huamn mnid deos not raed
ervey lteter by istlef, but the wrod as a
wlohe.
11
12
13
Psychophysics
A study of the relationship between physical
characteristics of stimuli and our psychological
experience with them.
Physical World
Psychological World
Light
Brightness
Sound
Volume
Pressure
Weight
Sugar
Sweet
14
The Stroop Task
Source: Stroop, J.R. (1935). "Studies of Interference in Serial Verbal Reactions." Journal of Experimental
Psychology, 18, 643-662.
Name the color of the font in which each word is
presented as rapidly as you can
15
Thresholds
Proportion of “Yes” Responses
1.00
0.50
0.00
Absolute Threshold: Minimum stimulation needed
to detect a particular stimulus 50% of the time.
0
5
10
15
20
Stimulus Intensity (lumens)
25
16
18
Sensory Thresholds
Vision
A candle flame seen at 30
mi. on a clear, dark night
Hearing The tick of a watch under
quiet conditions at 20 ft.
Taste
One teaspoon of sugar in
2 gallons of water
Smell
1 drop of perfume diffused
into the entire volume of a
3 room apartment
Touch
The wing of a bee falling on
your cheek from a height of
1 cm
20
Why Does the “Absolute”
Threshold Vary?
- Signal Detection
• Sensitivity:
– Intensity of the signal.
– Capacity of sensory systems.
– Amount of background stimulation, or “noise.”
• Response criterion reflects one’s
willingness to respond to a stimulus.
– Influenced by motivation and expectancies.
21
Subliminal Threshold
Subliminal Threshold:
When stimuli are below
one’s absolute threshold
for conscious
awareness.
22
Thinking Critically: Can Subliminal
Stimuli Influence Your Behavior?
• What am I being asked to believe or
accept?
– Subliminal stimuli can influence behavior.
• What evidence is available to support the
assertion?
– Can have at least a temporary impact on
judgment and emotion.
– No evidence as to the effectiveness of
subliminal advertising or value of subliminal
self-help tapes.
26
Thinking Critically: Subliminal
Stimuli Influence (cont’d.)
• What conclusions are most reasonable?
– Subliminal perception does occur, but has no
potential for “mind control.”
– Subliminal effects are usually small and shortlived.
– Effects mainly affect simple judgments and
general measures of overall arousal.
27
Subliminals
28
29
30
31
32
33
34
35
36
• http://www.ted.com/talks/michael_shermer
_on_believing_strange_things.html
• http://www.youtube.com/watch?v=Gv6ZAM5gds
• http://jeffmilner.com/backmasking/index.ht
ml
37
Judging Differences Between
Stimuli
• Difference Threshold or Just-Noticeable
Difference (JND)
• JND = Smallest detectable difference in
stimulus energy.
• JND determined by two factors:
– How much of a stimulus was there to begin
with?
– Which sense is being stimulated?
38
Weber’s Law (AP only)
• Law States That JND = KI
– K is the Weber’s constant for a particular
sense (each sense has its own K value.)
– I is the amount, or intensity, of the stimulus.
39
Sensory Adaptation
Diminished sensitivity as a consequence of
constant stimulation.
Put a band aid on your arm and after awhile
you don’t sense it.
40
Now you see, now you don’t
41
Transduction
In sensation, the transformation of stimulus energy
(sights, sounds, smells) into neural impulses.
42
Both Photos: Thomas Eisner
The Stimulus Input: Light Energy
Visible
Spectrum
43
Wavelength (Hue)
Hue (color) is the
dimension of
color determined
by the
wavelength of
the light.
Wavelength is
the distance from
the peak of one
wave to the peak
of the next.
44
Wavelength (Hue)
Violet
Indigo
400 nm
Short wavelengths
Blue
Green
Yellow
Orange
Red
700 nm
Long wavelengths
Different wavelengths of light result
in different colors.
45
Intensity (Brightness)
Intensity:
Amount of
energy in a
wave
determined by
the amplitude.
It is related to
perceived
brightness.
46
The Lens
Lens: Transparent
structure behind the
pupil that changes shape
to focus images on the
retina.
Accommodation: The
process by which the
eye’s lens changes shape
to help focus near or far
objects on the retina.
47
Retina
Retina: The lightsensitive inner
surface of the eye,
containing receptor
rods and cones in
addition to layers of
other neurons
(bipolar, ganglion
cells) that process
visual information.
48
Optic Nerve, Blind Spot & Fovea
Optic nerve: Carries neural impulses from the eye to the
brain.
Blind Spot: Point where the optic nerve leaves the eye
because there are no receptor cells located there.
Fovea: Central point in the retina around which the eye’s
cones cluster.
49
http://www.bergen.org
The Eye
50
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.
51
52
Retina’s Reaction to Light- Receptors
 Rods
 peripheral retina
 detect black, white and gray
 twilight or low light
 Cones
 near center of retina
 fine detail and color vision
 daylight or well-lit conditions
53
Rod Serling from the B&W Twilight Zone, Rod = B & W
Cone = Color
54
Photoreceptors
55
E.R. Lewis, Y.Y. Zeevi, F.S Werblin, 1969
Rods
Cones
56
57
Bipolar & Ganglion Cells
Bipolar cells receive
messages from
photoreceptors and
transmit them to
ganglion cells,
which converge to
form the optic
nerve.
58
59
Visual Information Processing
Optic nerves connect to the thalamus in the
middle of the brain, and the thalamus connects to
the visual cortex.
60
Feature Detection
Ross Kinnaird/ Allsport/ Getty Images
Nerve cells/neurons in the visual cortex respond
to specific features, such as edges, angles, and
movement.
61
A Feature detector
62
Shape Detection
Ishai, Ungerleider, Martin and Haxby/ NIMH
Specific combinations of temporal lobe activity
occur as people look at shoes, faces, chairs and
houses.
63
Visual Information Processing
Processing of several aspects of the stimulus
simultaneously is called parallel processing. The
brain divides a visual scene into subdivisions such
as color, depth, form, movement, etc.
64
Tim Bieber/ The Image Bank
From Sensation to Recognition
65
Visual Information
Processing
 Trichromatic (three color) Theory
 Young and Helmholtz
 three different retinal color receptors
 red
 green
 blue
66
Photoreceptors
Blue
Cones
MacNichol, Wald
and Brown (1967)
measured directly
the absorption
spectra of visual
pigments of single
cones obtained from
the retinas of
humans.
Short
wave
Green
Cones
Medium
wave
Red
Cones
Long
wave
67
Relative Responses
of Three Cone Types to Different
Wavelengths of Light
68
Color Blindness
Genetic disorder in which people are blind to
green or red colors. This supports the
Trichromatic theory.
Ishihara Test
69
72
73
74
75
Opponent Process Theory
Hering proposed that we process four primary
colors combined in pairs of red-green, blueyellow, and black-white.
76
Opponent Colors
Gaze at the middle of the flag for about 60
Seconds. When it disappears, stare at the dot and report
whether or not you see Britain's flag.
77
Complementary
Afterimages
Gaze at the middle of the flag for about 60
Seconds. When it disappears, stare at the dot and report
whether or not you see America's flag.
78
79
EXPLORING
PSYCHOLOGY
(7th Edition in Modules)
David Myers
PowerPoint Slides
Aneeq Ahmad
Henderson State University,
Amy Jones, Bernstain, Garber
edits
Worth Publishers, © 2008
80
Intensity (Brightness)
Blue color with varying levels of intensity.
As intensity increases or decreases, blue color
looks more “washed out” or “darkened.”
81
82