Sensation & Perception
To represent the world, we must detect physical
energy (a stimulus) from the environment and
convert it into neural signals. This is a process
called sensation.
When we select, organize, and interpret our
sensations, the process is called perception.
1
Bottom-up Processing
Analysis of the stimulus begins with the sense receptors
and works up to the level of the brain and mind.
ASSOCIATE WITH SENSATION.
Letter “A” is really a black blotch broken down into
features by the brain that we perceive as an “A.”
2
Top-Down Processing
Information processing guided by higher-level
mental processes as we construct perceptions,
drawing on our experience and expectations.
ASSOCIATE WITH PERCEPTION (schemas also)
THE CHT
3
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
4
Subliminal Threshold
Subliminal Threshold: When
stimuli are below one’s absolute
threshold for conscious
awareness.
Kurt Scholz/ Superstock
5
SUBLIMINAL STIMULATION
The priming effect = the activation, often
unconsciously, of certain associations, thus
predisposing one’s perception, memory, or
response.
6
WEBER’S LAW
•Weber’s Law JND = KI. To be perceived as different,
two stimuli must differ by a constant minimum
percentage.
K = constant (see chart from Bernstein)
I = intensity
•Major principle: Our thresholds for detecting
differences are a roughly constant proportion of the size
of the original stimulus)
7
Signal Detection Theory (SDT)
Predicts how and when we detect the presence
of a faint stimulus (signal) amid background
noise (other stimulation). SDT assumes that
there is no single absolute threshold and
detection depends on:
Carol Lee/ Tony Stone Images
Person’s experience
Expectations
Motivation
Level of fatigue
8
SDT Matrix
The observer decides whether she hears the tone
or not, based on the signal being present or not.
This translates into four outcomes.
Decision
Yes
No
Present
Hit
Miss
Absent
False
Alarm
Correct Rejection
Signal
9
Sensory Adaptation
Diminished sensitivity as a consequence of constant
stimulation (unchanging stimulus).
Put a band aid on your arm and after awhile
you don’t sense it.
10
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.
11
Intensity (Brightness)
Intensity
Amount of
energy in a wave
determined by
the amplitude. It
is related to
perceived
brightness.
12
The Eye
13
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.
14
The Lens
Nearsightedness: A
condition in which
nearby objects are seen
more clearly than
distant objects.
Farsightedness: A
condition in which
faraway objects are
seen more clearly than
near objects.
15
Parts of the eye
1.
2.
3.
4.
Cornea: Transparent tissue where light enters the
eye.
Iris: Muscle that expands and contracts to change
the size of the opening (pupil) for light.
Lens: Focuses the light rays on the retina.
Retina: Contains sensory receptors (rods and cones)
that process visual information and send it to the
brain. Rods and cones contain photopigment –
chemicals that respond to light.
16
RETINAL PROCESSING
The axons of the ganglion cells form the optic nerve
(where it leaves the eye, a blind spot is created.
Ganglion cells have a center surround receptive
field. How the light hits the center vs the outside
helps us to see edges and contrasts between light
and dark.
17
Visual Information Processing
Optic nerves connect to the thalamus (specific region =
LGN the lateral geniculate nucleus) in the middle of the
brain, and the thalamus connects to the visual cortex.
18
Feature Detection
Ross Kinnaird/ Allsport/ Getty Images
Nerve cells in the visual cortex respond to
specific features hierarchically, such as edges,
angles, and movement. Discovered by Hubel
and Wiesal – won Nobel Prize
19
Visual Information Processing
Processing of several aspects of the stimulus
simultaneously is called parallel processing (the
opposite of serial processing). The brain divides a visual
scene into subdivisions such as color, depth, form and
movement etc.
20
SUMMARY
Color processing has two stages.
The retina’s red, green, and blue cones
respond to different color stimuli in different
ratios (Trichromatic Theory).
Then, the nervous system’s ganglion cells with
their center surround feature process
information on its way to the visual cortex
(Opponent-Process Theory) . Afterimage
demonstrates
21
VISUAL CAPTURE
• How important is vision?
• Is vision more important than the other
senses?
22
Frequency (Pitch)
Frequency (pitch):
The dimension of
frequency
determined by the
wavelength of
sound.
Wavelength: The
distance from the
peak of one wave
to the peak of the
next.
23
Intensity (Loudness)
Intensity (Loudness):
Amount of energy in a
wave, determined by
the amplitude, relates
to the perceived
loudness.
24
The Ear
Dr. Fred Hossler/ Visuals Unlimited
25
Cochlea
Cochlea: Coiled, bony, fluid-filled tube in the
inner ear that transforms sound vibrations to
auditory signals.
26
AUDITION
• The cilia or hair cells, respond to ripples in the basilar
membrane.
• Auditory nerve sends message to thalamus and then
temporal lobe’s auditory cortex
• Loudness determined by the number of activated hair cells.
27
Theories of Audition
Von Helmholtz’s Place Theory suggests that
sound frequencies stimulate the basilar
membrane at specific places resulting in
perceived pitch. Best explains sensing high
pitches.
http://www.pc.rhul.ac.uk
28
Theories of Audition
Frequency Theory states that the rate of nerve impulses
traveling up the auditory nerve matches the frequency
of a tone, thus enabling us to sense its pitch. Best
explains low pitches.
Sound
Frequency
Auditory Nerve
Action Potentials
100 Hz
200
29
Theories of Audition
• Volley principle: subset of Frequency
theory – Alternating firing of neural cells
allows to sense very high frequencies.
• Combination of place and frequency
theories best explains intermediate range
30
Localization of Sounds
Because we have two ears, sounds that reach
one ear faster than the other ear cause us to
localize the sound.
31
Localization of Sound
Timing and Intensity help in localizing sound
•
The brain uses parallel processing - processing
timing differences and intensity differences as
well as other features of sound such as contrast
SIMULTANEOUSLY
32
Hearing Loss
Conduction Hearing Loss: Hearing loss caused
by damage to the mechanical system (3 bones)
that conducts sound waves to the cochlea.
Sensorineural Hearing Loss Hearing loss caused
by damage to the cochlea’s receptor cells or to
the auditory nerve, also called nerve deafness.
33
NERVE DEAFNESS
• Often linked to heredity, aging and prolonged exposure to
loud sounds
• These tissues cannot be regenerated once dead
• Digital hearing aids little help for nerve deafness
34
SENSORY COMPENSATION
• DEFINITION: slight enhancement of other
senses
• Example: people with aphasia (inability to
express language) are more accurate with
nonverbal cues
35
Other Important Senses
Bruce Ayers/ Stone/ Getty Images
The sense of touch (essential to development) is a mix
of four distinct skin senses—pressure, warmth, cold,
and pain.
36
Skin Senses
Only pressure has identifiable receptors. All
other skin sensations are variations of pressure,
warmth, cold and pain.
Pressure
Burning hot
Vibration
Vibration
Cold, warmth and pain
37
TOUCH AND
TEMPERATURE = SOMATIC
SENSES
1. The stimulus and receptors for touch
– a.when hairs on skin are bent, they deform the
skin beneath them
– b.receptors that transduce this deformation into
neural activity are in or near the skin
2. Some areas are more sensitive because they have
more receptors
Adaptation – change is the most important
information
38
PAIN
• 1.
Pain is necessary!
– a. Different thresholds for pain; hyperalgesia:
extreme sensitivity
– b. Damage = release of bradykinin, a chemical
that fits into specialized receptors in pain
neurons
– C .Mylinated to carry message faster (A. Delta);
C fibers carry dull pain
– d. Emotional aspects of pain – expectation
– e. Natural analgesics = endorphins and serotonin
39
Gate-Control Theory
Melzak and Wall (1965, 1983) proposed that our
spinal cord contains neurological “gates” that
either block pain or allow it to be sensed.
Gary Comer/ PhototakeUSA.com
40
GUSTATION
• Receptors for taste are located in the taste buds
grouped together in papillae
• 10,000 in mouth, mostly on the tongue, also in
back of tongue
41
GUSTATION
• Gustation is a chemical sense
– Taste receptor cells project hairs into pores
– Can reproduce themselves, but decrease
with age
Flavor: Smell + taste, also affected by
temperature
42
OLFACTION
• Odors are sensed in the upper part of the nose,
where receptors detect molecules that pass into the
moisture of the lining of the nose.
• They are the only neurons which are exposed and
replace themselves
• Diminish with age, smoking, Alzheimer’s,
Parkinson’s, and alcoholism
43
OLFACTION
• Olfaction is a dual sense because we detect odors that are
either
•
Internal entering through the mouth, or
•
External entering through the nose
• We have particular receptors for particular smells
• Axel and Beck received the Nobel prize for discovering
receptor proteins embedded in surface of nasal cavity
• Odors trigger a combination of receptors, then interpreted
by olfactory cortex
44
PROPRIOCEPTION
• Sensory systems giving information about the
position of the body and what each part is
doing
• Sensorimotor co-ordination
45
Body Position and Movement
The sense of our body parts’ position and
movement is called kinesthesis. The vestibular
sense monitors the head (and body’s) position.
Bob Daemmrich/ The Image Works
http://www.heyokamagazine.com
Whirling Dervishes
Wire Walk
46
VESTIBULAR SYSTEM
• Vestibular System = information about the
position and movement of the head
• Located in Inner Ear
• Semicircular Canals
• Vestibular sacs - connect canals with cochlea
• Fluid and otoliths (crystals) on hair
47
Smell and Memories
The brain region for
smell (in red) is closely
connected with the
brain regions involved
with memory (limbic
system).
48
VESTIBULAR SENSE
• Movement influences fluid in sacs and canals
• Neural connections with
• Cerebellum = balance
• ANS = affects digestive system
• Muscles of eyes (vestibular-ocular reflex)
49
iClicker Questions for
Psychology, 8th Edition
by David G. Myers
Karla Gingerich, Colorado State University
Chapter 5: Sensation
50
1.Racial and ethnic stereotypes can
sometimes bias our perceptions of
others' behaviors. This best
illustrates the impact of:
A.
B.
C.
D.
retinal disparity.
interposition.
top-down processing.
perceptual adaptation.
51
2.The fact that perceptions
involve more than the sum of
our sensations best illustrates
the importance of:
A.
B.
C.
D.
top-down processing.
interposition.
retinal disparity.
visual capture.
52
3.Which of the following is TRUE?
A. Humans cannot sense stimuli below the absolute
threshold.
B. Humans cannot be affected by stimuli below the
absolute threshold at all.
C. Stimuli presented below the absolute threshold
can have a subtle, brief effect on behavior.
D. Stimuli presented below the absolute threshold
exert a strong, powerful effect on behavior.
53
4.If you move your watchband up
your wrist an inch or so, you will
feel it for only a few moments.
This best illustrates:
A.
B.
C.
D.
parallel processing.
accommodation.
sensory adaptation.
Weber's law.
54
5.As we look at a flower, the
intensity of the color we see is
related to the light wave’s:
A.
B.
C.
D.
amplitude.
hue.
length.
placement on the spectrum.
55
6.The eye’s “blind spot” is related
to:
A. light rays focusing too far in front of the
retina.
B. light rays focusing too far behind the retina.
C. a cluster of cells around the fovea which
contains cones, but no rods.
D. an area without receptor cells where the
optic nerve leaves the eye.
56
7.Rather than saying a person is
“colorblind,” it would be more
accurate to say that the person:
A. has a blind spot.
B. lacks red- or green-sensitive cones.
C. is experiencing an overstimulation of the
red- and green-sensitive cones.
D. has an excess of blue-sensitive cones.
57
8.The malleus, incus, and stapes
are found in the:
A.
B.
C.
D.
middle ear.
inner ear.
cochlea.
outer ear.
58
9.What is umami?
A. a taste sensation for which researchers
recently discovered receptors on the tongue
B. receptors on the tongue that respond only to
bitter tastes
C. receptors on the tongue that allow us to taste
nutrients in food, such as proteins and
vitamins
D. a condition in which there is a loss of the
sensation of taste
59
10.As a professional chef, which of
the following sensations would you
rely on most?
A.
B.
C.
D.
hearing
seeing
balance
smell
60
Critical Thinking Questions
61
11.Which of the following activities
requires you to use the absolute
threshold for sensation?
A. telling the difference between sweet and
salty
B. detecting a tiny, faint light on a radar screen
C. deciding if two glasses contain the same
amount of water
D. telling if your guitar is in tune
62
12.You are going to design an experiment to
determine whether there are special areas on
the tongue to detect the taste of sweet, or
whether the taste can be detected in all areas
of the tongue. Which of these must be done
before you can start the experiment?
A.
B.
C.
D.
operationally define sweet.
pick out subjects who like sweet tastes.
pick out the items that you will use for sweet tastes.
none of these are necessary.
63
13.Your roommate, who has trouble
understanding Weber’s Law, asks
you, “How different do two stimuli
need to be, in order for a person to
notice the difference?” You explain
that:
A. the stimuli must differ by at least ten percent.
B. the difference threshold decreases with the
magnitude of the stimulus.
C. the minimum difference needed for detection
depends on the type of stimulus.
D. Weber’s Law does not address this issue.
64
14.Researcher James Hixby (2001)
stated, “We can tell if a person is
looking at a shoe, a chair, or a face,
based on the pattern of their brain
activity.” This statement is relevant
to:
A.
B.
C.
D.
sensory adaptation.
feature detection.
opponent-process theory.
place theory.
65
15.Racial and ethnic stereotypes
can sometimes bias our perceptions
of others' behaviors. This best
illustrates the impact of:
A.
B.
C.
D.
retinal disparity.
interposition.
top-down processing.
perceptual adaptation.
66
Perception
Chapter 6
67
Perception
The process of selecting, organizing, and
interpreting sensory information, which
enables us to recognize meaningful objects
and events
(Top down processing).
68
Selective Attention
Perceptions about objects change from
moment to moment. Example: the Stroop
Task - what is it?
Necker Cube
69
Inattentional Blindness
Daniel Simons, University of Illinois
Inattentional blindness refers to the
inability to see an object or a person in
our midst.
70
Change Blindness
Change blindness is a form of inattentional
blindness in which two-thirds of individuals
giving directions failed to notice a change in the
individual asking for directions.
© 1998 Psychonomic Society Inc. Image provided courtesy of Daniel J. Simmons.
71
POP-OUT
• A STRIKINGLY
DISTINCT
STIMULUS DRAWS
OUR EYE
72
SELECTIVE ATTENTION
• Attentional resources are limited
• Overt vs covert orienting
• When can we divide attention?
– How automatic?
– Different kinds of attentional resources
– Stress narrows attention
73
Perceptual Illusions
Illusions provide good examples in
understanding how perception is organized.
Studying faulty perception is as important as
studying other perceptual phenomena. MullerLyer Illusion:
Line AB is longer than line BC.
74
Perceptual Organization
When vision competes with our other senses,
vision usually wins – a phenomena called visual
capture.
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.
75
PERCEPTUAL
ORGANIZATION
• Sensation (bottom up processing) and
Perception (top down processing) blend into
one continuous process
• Fundamental point: We constantly filter
sensory information and infer perceptions in
ways that make sense to us. Mind matters.
76
Form Perception
Organization of the visual field into objects
(figures) that stand out from their surroundings
(ground). Another example: cocktail party
phenomena
Time Savings Suggestion, © 2003 Roger Sheperd.
77
REVERSIBLE FIGURE
GROUND
• Reversible figureground illusions
demonstrate that the
same stimulus can
trigger more than
one perception.
78
Grouping
After distinguishing the figure from the ground,
our perception needs to organize the figure into
a meaningful form using grouping rules (Gestalt
psychologists).
79
OTHER GROUPING
PRINCIPLES
• LIKLIHOOD PRINCIPLE: we tend to
perceive objects in the way that
experience tells us is the most likely
physical arrangement
• Auditory scene analysis
– Sound localization
– Visual capture
80
Depth Perception
Innervisions
Depth perception enables us to judge distances.
Gibson and Walk (1960) suggested that human
infants (crawling age) have depth perception.
Depth perception appears to be innate, amplified by
experience
Visual Cliff
81
DEPTH PERCEPTION
• Two dimensional images fall on our retina,
how do we see three dimensionally?
• Depth perception (seeing objects in three
dimensions) allows us to judge distance
82
Binocular Cues
Retinal disparity: Images from the two eyes differ.
Brain compares these images, their differences provide
cues to relative distance of different objects
83
Binocular Cues
Convergence: Neuromuscular cues. When two eyes
move inward (towards the nose) to see near objects and
outward (away from the nose) to see faraway objects.
Accomodation – muscles surrounding the lens
tightening
84
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.
85
Monocular Cues
Interposition: Objects that occlude (block) other
objects tend to be perceived as closer.
Rene Magritte, The Blank Signature, oil on canvas,
National Gallery of Art, Washington. Collection of
Mr. and Mrs. Paul Mellon. Photo by Richard Carafelli.
86
Monocular Cues
Relative Clarity: Because light from distant objects
passes through more light than closer objects, we
perceive hazy objects to be farther away than
those objects that appear sharp and clear.
87
Monocular Cues
Texture Gradient: Indistinct (fine) texture
signals an increasing distance.
© Eric Lessing/ Art Resource, NY
88
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 Shaun P. Vecera, Ph. D.,
adapted from stimuli that appered in Vecrera et al., 2002
89
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.
90
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.
© The New Yorker Collection, 2002, Jack Ziegler
from cartoonbank.com. All rights reserved.
91
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 Shape From Shading” by Vilayaur
S. Ramachandran. © 1988 by Scientific American, Inc.
All rights reserved.
92
Motion Perception
Motion Perception: Objects traveling towards us
grow in size (looming) and those moving away
shrink in size. The same is true when the observer
moves to or from an object.
93
Apparent Motion
Phi Phenomenon: When lights flash at a certain
speed they tend to present illusions of motion.
Neon signs use this principle to create motion
perception.
Two lights
one
after the Illusion
other. of motion.
One light jumping
from flashing
one point
to another:
94
Perceptual Constancy
Perceiving objects as unchanging even as
illumination and retinal images change. Brain needs
to recognize the object without being deceived by
changes. Perceptual constancies include
constancies of shape and size.
Shape Constancy
95
Size Constancy
Stable size perception amid changing size of the
stimuli.
Size Constancy
96
Size-Distance Relationship
The distant monster (below, left) and the top red bar
(below, right) appear bigger because of distance cues.
Cultural experience also influences.
Alan Choisnet/ The Image Bank
From Shepard, 1990
97
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
98
Lightness Constancy
The color and brightness of square A and B are the
same. Depends on relative luminance - the amount of 99
light an object reflects relative to its surroundings.
Color Constancy
Perceiving familiar objects as having consistent
color even when changing illumination filters
the light reflected by the object.
Color Constancy
100
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?
101
Sensory Deprivation
Kittens raised without
exposure to horizontal
lines later had difficulty
perceiving horizontal
bars. Influence of
critical periods shown.
Blakemore & Cooper (1970)
102
Perceptual Set
A mental predisposition to perceive one thing
and not another. What you see in the center
picture is influenced by flanking pictures.
Whisper Down the Lane example.
From Shepard, 1990.
103
Allport and Postman
• LEVELING - perceiver drops certain
details because they don’t “fit”
• SHARPENING - details consistent with
values and interests are emphasized
• ASSIMILATION - padding and
organization used to make central
theme fit subject’s expectations
104
PERCEPTUAL SET
What determines perceptual set?
• Through experience we form concepts, or
schemas, that organize and interpret unfamiliar
information.
– Example: a child’s simplified drawing of people
• Our innate schemas for faces primes us, especially
attune to the eyes and mouth
105
Schemas
Schemas are concepts that organize and
interpret unfamiliar information.
Courtesy of Anna Elizabeth Voskuil
Children's schemas represent reality as well as their
abilities to represent what they see.
106
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.
107
Perception Revisited
Is perception innate or acquired?
108
Perception & Human Factors
Human Factor Psychologists design machines
that assist our natural perceptions.
Courtesy of General Electric
Photodisc/ Punchstock
The knobs for the stove burners on the right are easier to
understand than those on the left.
109
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.
110
iClicker Questions for
Psychology, 8th Edition
by David G. Myers
Karla Gingerich, Colorado State University
Chapter 6: Perception
111
1.As you talk with a friend at a
party, her voice is distinct from all
the other voices you hear. This
illustrates the perceptual principle
of:
A.
B.
C.
D.
grouping.
proximity.
closure.
figure-ground.
112
2.The way in which you quickly
group the individual letters in this
test item into separate words best
illustrates the principle of:
A.
B.
C.
D.
closure.
proximity.
continuity.
convergence.
113
3.Makers of 3-D movies rely most
heavily on:
A.
B.
C.
D.
the visual cliff.
the Müller-Lyer illusion.
retinal disparity.
shape constancy.
114
4.After hearing that Bryce had served
a prison sentence, Janet began to
perceive his friendly behavior as
insincere and manipulative. This best
illustrates the impact of:
A.
B.
C.
D.
perceptual sets.
visual capture.
bottom-up processing.
sensory adaptation.
115
5.Which is easier to recognize?
A.
B.
C.
D.
an actual picture of a face
the caricature of the face
the anticaricature of the face
an upside-down picture of the face
116
6.If a person were able to sense that
his friend’s dog was lost and needed
help, this person would be said to
have:
A.
B.
C.
D.
psychokinesis.
telepathy.
precognition.
clairvoyance.
117
Critical Thinking Questions
118
6.As we perceive the environment, we use
Gestalt principles of good form to help
organize things into meaningful groups and
forms. In observing a football game on TV
we are immediately able to recognize the
players as members of their respective
teams, regardless of their positions on the
field. Which Gestalt principle is most
responsible
for
this
ability?
A. closure
B. proximity
C. similarity
D. continuity
119
7.In the same football game, we watch as a
team attempts a field goal. Since the goal
posts are distant and the time to make a
decision is short, the referee must use
many perceptual cues to decide whether
the kick is good or not. One important
ability is depth perception. Which of the
following cues might be most helpful in
deciding whether the field goal is
A. linear perspective successful?
B. motion parallax
C. convergence
D. interposition
120
8.You are an artist and you are interested
in completing a painting that gives a threedimensional appearance. You want to
show a beach in the foreground of the
painting, people swimming in the ocean,
and sailboats in the distance. Which
perceptual principles will be most helpful as
you complete your painting?
A.
B.
C.
D.
binocular depth cues
monocular depth cues
Gestalt principles of proximity and continuity
perceptual principles only operate in “real life” situations
121
9.You are most likely to observe
the phi phenomenon while:
A. looking at a string of Christmas tree lights that
blink quickly in succession.
B. staring at a Necker cube.
C. comparing the size of the moon while its in the
sky to its size near the horizon.
D. attempting to catch fly ball that is quickly
coming toward you.
122