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SENSATION AND
PERCEPTION
CHAPTER 6
AP Psychology ~ Ms. Justice
BIG IDEAS
Seeing
the World: Some Basic Principles
Thresholds
Vision
Hearing
Other Important Senses
Perceptual Organization
Perceptual Interpretation
Is There Extrasensory Perception?
1: What are sensation and perception?
What do we mean by bottom-up
and top-down processing?
SENSATION & PERCEPTION
How do we construct our
representations of the external world?
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.
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.”
We process this way when we have no prior knowledge:
we start at the bottom and work our way up.
TOP-DOWN PROCESSING
Information processing guided by higher-level
mental processes as we construct perceptions,
drawing on our experience and expectations.
THE CHT
We process this way when we have prior knowledge: we
start at the top and have to work to process details.
MAKING SENSE OF COMPLEXITY
Our sensory and perceptual processes work
together to help us sort out complex images.
“The Forest Has Eyes,” Bev Doolittle
2: What are absolute and difference
thresholds, and do stimuli below the
absolute threshold have any influence?
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
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
SUBLIMINAL THRESHOLD
Subliminal Threshold: When
stimuli are below one’s absolute
threshold for conscious
awareness.
While much of our information
processing occurs
automatically (sensation),
claims of subliminal persuasion
have been discounted through
research.
WEBER’S LAW
Two stimuli must differ by a constant minimum
percentage (rather than a constant amount), to be
perceived as different. Weber fraction: k = dI/I.
Stimulus
Constant (k)
Light
8%
Weight
2%
Tone
0.3%
3: What is the function of
sensory adaptation?
SENSORY ADAPTATION
Sensory adaptation is the diminishing sensitivity to an
unchanging stimulus.
After constant exposure to a stimulus, our nerve cells
fire less frequently.
Put a band aid on your arm and after
awhile you don’t sense it.
Sensory adaptation offers the freedom to focus on informative
changes in our environment: We perceive the world not exactly
as it is, but as it is useful for us to perceive it.
4: What is the energy that we
see as visible light?
TRANSDUCTION
Transduction is the
transformation of stimulus
energy (sights, sounds,
smells) into neural impulses
our brains can interpret.
What we see as visible light
is but a thin slice of the
whole spectrum of
electromagnetic radiation.
Visible
Spectrum
PHYSICAL CHARACTERISTICS OF LIGHT
Two physical characteristics
of light help determine our
sensory experience of them:
1.
Wavelength (the distance
from one wave peak to
the next) determines hue
or color
2.
Intensity (the amount of
energy in light waves)
influences brightness
WAVELENGTH (HUE/COLOR)
Violet
Indigo
Blue
Green
Yellow
Orange
Red
700 nm
400 nm
Short wavelengths
Long wavelengths
INTENSITY (BRIGHTNESS)
Blue color with varying levels of intensity.
As intensity increases or decreases, blue color
looks more “washed out” or “darkened.”
5: How does the eye transform
light energy into neural
messages?
THE EYE
Label the diagram of the eye, providing a brief
description of what each part of the eye does.
(page 237)
Label the cross section of the retina, explaining
how light entering the eye is transformed into
a neural message. (page 238)
THE EYE
TEST YOUR BLIND SPOT
Use your textbook – PAGE 239.
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.
PHOTORECEPTORS
E.R. Lewis, Y.Y. Zeevi, F.S Werblin, 1969
Table 6.1: page 239
6: How does the brain process
visual information?
VISUAL INFORMATION


Ganglion axons forming the optic nerve run to the
thalamus, where they synapse with neurons that run to the
visual cortex.
Any given retinal
area relays its
information to a
corresponding
location in the
visual cortex, in
the occipital lobe
at the back of
your brain.
Figure 6.10, page 240
SHAPE DETECTION
Ishai, Ungerleider, Martin and Haxby/ NIMH
Specific combinations of temporal lobe activity
occur as people look at shoes, faces, chairs and
houses.
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.
FROM SENSATION TO RECOGNITION
Figure 6.13
p. 243
7: What theories help us
understand color vision?
COLOR VISION
Young-Helmholtz
trichromatic theory:
Thomas Young and Hermann von
Helmholtz suggested that the eye must
contain three receptors that are sensitive to
red, blue and green colors in the 19th
century. Years later, researchers confirmed
this theory.
The
retina has three types of color
receptors, each sensitive to one of three
colors.
When
we stimulate combinations of these
cones, we see other colors.
For
example, when both red-sensitive and
green-sensitive cones are stimulated, we see
yellow.
COLOR BLINDNESS
Genetic disorder in which people are blind to
green or red colors. This supports the
Trichromatic theory.
Ishihara Test
OPPONENT COLORS
Gaze at the middle of the flag for about 30
Seconds. When it disappears, stare at the dot and report
whether or not you see Britain's flag.
8: What are the characteristics of
air pressure waves that we hear
as sound?
AUDITION



Audition, or hearing, is highly adaptive.
We hear a wide range of sounds, but we hear
best those sounds with frequencies in a range
corresponding to that of the human voice.
We are also remarkably
attuned to variations in
sounds: For example, we
easily detect differences
among thousands of
human voices.
SOUND CHARACTERISTICS
Sound waves are compressing and expanding air
molecules.
The
wave’s frequency, or
length, determine the pitch we
experience. Long waves have a
low frequency & pitch. Short
waves have a high frequency &
pitch.
The
wave’s intensity, or
strength, determines the
loudness we experience.
9: How does the ear transform
sound energy into neural
messages?
THE EAR
Sound waves are converted into neural activity:
Outer Ear: Collects and sends sounds to the eardrum.
Middle Ear: Chamber between eardrum and cochlea
containing three tiny bones (hammer, anvil, stirrup)
that concentrate the vibrations of the eardrum on the
cochlea’s oval window.
Inner Ear: Innermost part
of the ear, containing the
cochlea, semicircular
canals, and vestibular
sacs.
COCHLEA
Cochlea: Coiled, bony, fluid-filled tube in the inner ear
that transforms sound vibrations to auditory signals.
INTENSITY (LOUDNESS)
Intensity (Loudness):
Amount of energy in a
wave, determined by
the amplitude, relates
to the perceived
loudness.
LOUDNESS OF SOUND
Richard Kaylin/ Stone/ Getty Images
120dB
70dB
120dB
Page 248
10: What theories help us
understand pitch perception?
FREQUENCY (PITCH)
Pitch: The dimension of
frequency determined by the
wavelength of sound.
Frequency theory: The rate of
nerve impulses traveling up the
auditory nerve matches the
frequency of a tone; enabling us
to sense its pitch. Best explains
how we sense low pitches.
Place theory: links the pitch we hear with the place where the
cochlea's membrane is stimulated. Best explains how we sense
high pitches.
A combination of the two theories handle the pitches in the
intermediate range.
11: How do we locate sounds?
LOCALIZATION OF SOUNDS
Because we have two ears, sounds that reach one ear
faster than the other ear causes us to localize the
sound.
Your right ear would receive
a more intense sound from
this bell ringing, and it
would receive the sound
slightly sooner than your left
ear.
However, the intensity
difference and time lag are
extremely small.
12: What are the common causes
of hearing loss, and why does
controversy surround cochlear
implants?
HEARING LOSS & DEAF CULTURE



Conduction hearing loss: problems with the
mechanical system that conducts sound waves to
the cochlea
Sensorineural hearing loss: damage
to the cochlea’s hair cell receptors
or their associated nerves
(more common)
Cochlear implants: electronic
devices that translate sounds into
electric signals that convey some
information about sound
to the brain.
13: How do we sense touch and
our body’s position and
movement?
How do we experience pain?
TOUCH
Bruce Ayers/ Stone/ Getty Images
The sense of touch is a mix of four distinct skin
senses—pressure, warmth, cold, and pain.
BODY POSITION &MOVEMENT
The sense of our body parts’ position and movement
is called kinesthesis. The vestibular sense monitors
the head (and body’s) position (including balance).
Bob Daemmrich/ The Image Works
http://www.heyokamagazine.com
PAIN
Pain tells the body that something has gone wrong.
Usually pain results from damage to the skin and other
tissues. A rare disease exists in which the afflicted
person feels no pain: Ashlyn Blocker
GATE-CONTROL THEORY
Melzack 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
The “gate” is opened by the activity of pain signals
traveling up small nerve fibers, and is closed by
activity in large nerve fibers
or by information coming
from the brain.
BIOPSYCHOSOCIAL INFLUENCES
Figure 6.22: p. 257
PAIN CONTROL
Pain can be controlled by a number of therapies
including, drugs, surgery, acupuncture, exercise,
hypnosis, and even thought distraction.
Todd Richards and Aric Vills, U.W.
©Hunter Hoffman, www.vrpain.com
14: How do we experience taste?
TASTE
Traditionally, taste sensations consisted of sweet,
salty, sour, and bitter tastes. Recently, receptors for
a fifth taste have been discovered called “Umami”.
Sweet
Sour
Salty
Bitter
Umami
(Savory meat
taste: MSG)
SENSORY INTERACTION
When one sense affects another sense, sensory
interaction takes place. So, the taste of strawberry
interacts with its smell and its texture on the
tongue to produce flavor.
15: How do we experience smell?
SMELL
• Like taste, smell is a chemical sense.
• Odorants enter the nasal cavity to stimulate 5
million receptors to sense smell.
• We can detect 10,000 odors!
Figure 6.25
Page 261
SMELL AND MEMORIES
The brain region for
smell (in red) is closely
connected with the
brain regions involved
with memory (limbic
system).
That is why strong
memories are made
through the sense of
smell.
16: How did the Gestalt
psychologists understand
perceptual organization?
PERCEPTUAL ORGANIZATION
How do we form meaningful perceptions
from sensory information?
A group of German psychologists noticed
that when given a cluster of sensations
people tend to organize them into a gestalt,
or an organized, meaningful whole.
WHAT DO YOU SEE?
Necker Cube
p. 264
17: How do figure-ground and
grouping principles contribute to
our perceptions?
FORM PERCEPTION
Our brain must recognize objects as distinct from their
backgrounds:
 The objects are figures.
 Their surroundings are the grounds.
The same stimulus can trigger more than one perception, and
allow the figure-ground relationship to reverse.
Time Savings Suggestion, © 2003 Roger Sheperd.
GROUPING
After distinguishing the figure from the ground,
our perception needs to organize the figure into
a meaningful form using grouping rules.
GROUPING & REALITY
Although grouping principles usually help us construct
reality, they may occasionally lead us astray.
Both photos by Walter Wick. Reprinted from GAMES
Magazine. .© 1983 PCS Games Limited Partnership
p. 265 & 269
M.C. ESCHER
18: How do we see the world in
three dimensions?
DEPTH PERCEPTION
Depth perception –the ability to see objects in three
dimensions although the images that strike the
retina are two dimensional- it enables us to judge
distances.
Cat with
no depth
perception:
VISUAL CLIFF
Gibson and Walk (1960) suggested that human infants (crawling
age) have depth perception using the visual cliff demonstration:
BINOCULAR CUES
Binocular cues are depth cues that depend on two eyes.
Retinal disparity, which is the distance between the images
received from the two retinas, is a binocular cue that
allows us to perceive depth. The greater the disparity
between the two images, the closer the object.
MONOCULAR CUES
Monocular cues are depth cues that are available
to either eye alone.
Relative Size: If two objects are similar in size, we perceive the
one that casts a smaller retinal image to be farther away.
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.
MONOCULAR CUES
Relative Height: We perceive objects that are higher in our
field of vision to be farther away than those that are lower.
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.
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.
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.
19: How do we perceive motion?
PERCEIVING MOTION
Our brain computes motion based partly on its
assumption that shrinking objects are retreating and
enlarging objects are approaching. Large objects are also
perceived to be moving more slowly that smaller objects.
The brain will also perceive continuous movement in a
series of slightly varying images.
The illusion of movement is also created using the phi
phenomenon – when two adjacent stationary lights blink
on and off in quick succession
20: How do perceptual
constancies help us organize our
sensations into meaningful
perceptions?
PERCEPTUAL CONSTANCY
Regardless of our viewing angle, distance, and
illumination, the top-down processing ability called
perceptual constancy allows us to identify people and
objects in less time than it takes to draw a breath.
Sometimes an object
whose actual shape
cannot change seems
to change shape with
the angle of our view.
p. 269
COLOR CONSTANCY
Perceiving familiar objects as having consistent
color even when changing illumination filters
the light reflected by the object.
Color Constancy
SIZE-DISTANCE RELATIONSHIP
Experience tells us that a more distant object can
create the same size image as a nearer one only if
it is actually larger.
As a result, we perceive the more distant monster
and red bar as larger.
Alan Choisnet/ The Image Bank
From Shepard, 1990
p. 270
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
p. 271
AMES ROOM
p. 271
The Ames room is designed to demonstrate the sizedistance illusion.
LIGHTNESS CONSTANCY
The color and
brightness of
square A and B
are the same.
p. 271
21: What does research on sensory
restriction and restored vision reveal
about the effects of experience?
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.
not
this
guy
SENSORY DEPRIVATION & RESTORED VISION
How important is experience in shaping our
perceptual interpretation?
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).
FACIAL RECOGNITION
Courtesy of Richard LeGrand
We perceive and recognize individual faces as a whole.
The same top half of a face paired with two different bottom
halves causes us to see the identical top halves as different.
After blind adults
regained sight, they
were able to recognize
distinct features, but
were unable to
recognize faces.
22: How adaptable is our ability
to perceive?
PERCEPTUAL ADAPTATION
Courtesy of Hubert Dolezal
Perceptual adaptation - the
visual ability to adjust to an
artificially displaced or
inverted visual field
Experiments involving
inversion glasses reveal that
after about a week people can
adapt to the change, and even
ride a motorcycle, ski, and fly
an airplane
23: How do our expectations,
contexts, and emotions influence
our perceptions?
PERCEPTUAL SET
A perceptual set is a mental predisposition to
perceive one thing and not another (top-down
processing).
Through experience we form concepts, or schemas,
that organize and interpret unfamiliar information.
The human brain is a hypersensitive face detector –
we see faces in random configurations such as cloud
formations, rocks, the moon’s landscape, and food.
PERCEPTUAL SET
What you see in the center picture is influenced by
flanking pictures.
PERCEPTUAL SET
Other examples of perceptual set:
Dick Ruhl
Frank Searle, photo Adams/ Corbis-Sygma
(a) Loch ness monster or a tree trunk?
(b) Flying saucers or clouds?
CONTEXT EFFECTS
Context can radically
alter perception.
How tall is the
basketball player in
yellow?
He is actually 6’9”
But when compared
to 7’9” Sun Ming
Ming, he seems short!
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.
PERCEPTION REVISITED
Perception is a biopsychosocial phenomenon
Figure 6-50
p. 279
24: How do human factors
psychologists work to create userfriendly machines and work settings?
HUMAN FACTORS PSYCHOLOGISTS
These psychologists work with engineers to design
appliances, machines, and work settings that fit our
natural perceptions and inclinations.
25: What are the claims of ESP, and what
have most research psychologists
concluded after putting these claims to the
test?
IS THERE EXTRASENSORY PERCEPTION?
Perception without sensory input is called
extrasensory perception (ESP). A large percentage
of scientists do not believe in ESP.
CLAIMS OF ESP
1.
2.
3.
Telepathy: Mind-to-mind communication. One
person sending thoughts and the other
receiving them.
Clairvoyance: Perception of remote events,
such as sensing a friend’s
house on fire.
Precognition: Perceiving
future events, such as a
political leader’s death.
CLAIMS OF ESP
Most research psychologists are skeptical about
claims of ESP for two main reasons:
1. To believe in ESP you must believe that the brain
is capable of perceiving without sensory input.
2. Psychologists and parapsychologists have been
unable to replicate ESP phenomena under
controlled conditions
No psychic has been able to predict the outcome of a lottery
jackpot or to make millions on the stock market.
No psychic was able to predict 9/11, or to collect the $50
million reward for locating Osama bin Laden.

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