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CHAPTER 4
SENSATION AND PERCEPTION
1) Sensation and Perception:
The Basics
 Sensation: Raw information that
comes from the senses
What is this?
1.) Sensation and Perception:
The Basics
 Perception: The process through
which people take raw sensations
from the environment and give
them meaning, using knowledge,
experience, and understanding of
the world.
Perception = Sensation + Meaning
1.) Sensation and Perception:
The Basics
 Absolute Threshold:
The
weakest amount of stimulation
needed to detect a stimulus
50% of the time
1.) Sensation and Perception:
The Basics
 Examples of Absolute Thresholds
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Vision: A candle flame viewed from a distance
of about 30 miles on a dark night
Hearing: The ticking of a watch from about 20
feet away in a quiet room
Smell: About one drop of perfume diffused
throughout a small house
Taste: About 1 teaspoon of sugar dissolved in 2
gallons of water
Touch: The wing of a fly falling on a cheek from
a distance of about .4 inch (1 centimeter)
1.) Sensation and Perception:
The Basics
 Absolute Threshold are different for
people due to psychological and
biological factors.
 What
are some examples?
http://jeffmilner.com/backmasking/another-one-bites-the-dust-backwards.html
1.) Sensation and Perception:
The Basics
 Difference Threshold (A.K.A.: JND):
The minimum amount of difference
needed to detect a change in
stimulus 50% of the time
Can you detect the difference in color between these two hues?
1.) Sensation and Perception:
The Basics
 People’s difference thresholds vary
slightly
 Our difference threshold is partly
dependent on the size of the original
stimulus
 What
jobs would require a person to
have a small difference threshold?
1.) Sensation and Perception:
The Basics
 Signal-Detection Theory: The
idea that distinguishing sensory
stimuli takes into account not only
the strength of the stimuli but also
such elements as setting, one’s
physical state, mood and attitudes
1.) Sensation and Perception:
The Basics
 Our ability to distinguish between sensory
stimuli takes into account:

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Our motivation
Our expectations
Our learning
Our physical fatigue
The signal detection theory says that
distinguishing sensory stimuli takes into
account not only the strength of the stimuli
but also such elements as setting, ones’
physical state, mood, attitude, etc.
Provide an example of something that could
raise or lower your absolute threshold
Would your example raise or lower your
absolute threshold? (Circle raise or lower)
Example: I am on a diet and someone in the theatre
(3 rows ahead of me) is eating popcorn. I can smell the
popcorn.
Being on a diet lowers my absolute threshold for smell.
1.) Sensation and Perception:
The Basics
 Sensory Adaptation: The process by which
we become more sensitive to weak stimuli and
less sensitive to unchanging stimuli
Why does sensory adaptation occur?
Sensory adaptation allows us to detect
potentially important changes in our
surroundings while ignoring unchanging aspects
of them.
1.) Sensation and Perception:
The Basics
 We will never completely adapt to
extremely intense sensations such
as severe pain or freezing cold.
Why?
 This is adaptive because to ignore
such stimuli might be harmful or
even fatal.
2.) Vision
 Vision depends on the interaction
of the eye and the brain. The eyes
sense objects and convey this
information to the brain, where
visual perception takes place.
2.) Vision
 Light


Light is described in wavelengths
Not all wavelengths are visible to humans
2.) Vision
 Light
The colors of the visible spectrum from longest to
shortest wavelengths are:
Red
Orange
The mnemonic device to remember this is:
Yellow
ROY G. BIV
Green
Blue
Indigo
Violet
2.) Vision
 The Eye
The eye works much like a camera
does
2.) Vision
 Parts of the Eye
2.) Vision
 Parts of the eye
Pupil: An opening in the
eye just behind the
cornea, through which
light passes
2.) Vision
Parts of the eye
Lens: The transparent
structure behind the
pupil that focuses light
onto the retina
2.) Vision
 Parts of the Eye
Retina:
The surface at
the back of the eye
onto which the lens focuses
light rays
The retinal image is upside-down and reversed
2.) Vision
 Parts of the Eye
Iris: The part of the
eye that gives its color and
adjusts the amount of light
entering it
2.) Vision
 The Blind Spot:
The point at which the optic nerve
leaves the eye creating “blind” spot
because no receptor cells are
located there
2.) Vision
 Rods and Cones
 Rods: Retinal receptors that detect black,
white, and gray; they are necessary for
peripheral and twilight vision, when cones
don’t respond.
They are located around the peripheral of
the retina
2.) Vision
 Cones: Receptor cells that are
concentrated near the center of the
retina and that function in daylight or in
well-lit conditions. The cones detect
fine detail and give rise to color
sensations. They are concentrated at
the center of the retina (fovea)
2.) Vision
2.) Vision
 Visual Acuity: the sharpness of vision
Visual Acuity is determined by the
ability to see visual details in normal
light.
 Visual Acuity
Chart
is measure by a Snellen
2.) Vision
 Visual Acuity
 Nearsighted:
when you have to be
close to an object to make out its
details (you can see close but not
far).
 Farsighted: when you have to be
far away from an object to make out
its details (you can see far but you
can’t see close)
2.) Vision
Normal Vision
Nearsighted
When the image reaches
the retina, the rays are
spreading out, blurring
the image.
Farsighted
Light rays from
nearby objects come
into focus behind the
retina, resulting in
blurred images
2.) Vision
 Color Vision
 Complementary
Colors
Colors directly across from each
other on the color wheel
(Ex. = Blue/Yellow Red/Green)
 If the wavelengths of
complementary colors are mixed
gray is formed

www.exploratorium.edu/exhibits/f_exhibits.html
2.) Vision
 Color Blindness: People who do not have
normal color vision are said to be color blind
2.) Vision
 Color Blindness
 People
who are totally color blind
(this is rare) see only black and
white
 A more common type is red-green
color blindness where people have
a difficult time seeing shades of red
and green
2.) Vision
 Color Blindness
 More
men than woman are color
blind because it is a trait carried
on the X chromosome

1 in 200 men are colorblind but
only 1 in 20 women
3) Hearing
 The stimulus for hearing is sound
waves. These sounds waves move
in roughly the same fashion as do
light waves, however they have a
much slower range of speed
3) Hearing
 Pitch:
How high or how low the sound is
 Depends on its frequency ( the number
of cycles per second)
 The higher the frequency the higher the
pitch
 What are some sounds with a low pitch?
 What are some sounds with a high pitch?

3) Hearing
3) Hearing
 Loudness:
 Measure by decibels
 Determined by the height (amplitude) of
the sound wave.
 The higher the amplitude of the wave,
the louder the sound
 When sounds reach a decibel level
beyond 130Db, they can become painful
3) Hearing
3) Hearing
 “Oh Grandma, what big ears you
have.”
 “The better to hear you with my
dear.”
 True or false?
3) Hearing
 Parts of the Ear
Pinna:
the ear flap
3) Hearing
Ear Drum:
The Ear Drum is a piece of skin stretched over the entrance to the ear,
it vibrates to sound. As it vibrates it sends the sound to the 3 bones in
the inner ear
3) Hearing
Cochlea
Cochlea is the Greek word for “snail”. It is filled with fluid and
small hairs that vibrate to incoming sounds. These vibrations
generate neural impulses that are transmitted to the brain
3) Hearing
Auditory Nerve
The Auditory Nerve is a bundle of nerves carrying sound to the brain
3) Hearing
 Locating Sound
 The
placement of our ears allows
us to enjoy stereophonic hearing
(three-dimensional)
 If a sound is louder in our right ear
and reaches it before it reaches
our left ear, we perceive the sound
as coming from the right
3) Hearing
 Locating Sound:
It is difficult to locate sounds that
are directly in front, behind, or on
top of our ears because the sound
reaches both ears at the same time
3) Hearing
 Deafness
 About
2 million Americans are
deaf
 There are two basic types of
deafness
Conductive deafness
 Sensorineural deafness (nerve
deafness)

3) Hearing
 Conductive Deafness
 Occurs
due to damage to the
middle ear
 Since it is caused by the ear’s
inability to conduct vibrations it
can be helped by a hearing aid
which will amplify the vibrations
3) Hearing
 Sensorineural Deafness (Nerve
Deafness)
 Occurs
due to damage to the inner ear
 Could result from:
Disease
 Prolonged Exposure to very loud sounds
 Biological changes associated with age

3) Hearing
 Because it is due to damage to the inner ear,
a hearing aid will not be very helpful.
However, today cochlear implants are being used to help people with this
type of deafness
4) Perception
 Rules of Perceptual Organization
 The
organization of sensations into
perception was studied by the
Gestalt psychologists beginning in
the early 1900s
 Gestalt is a German word meaning
whole figure
 The Gestalt psychologists believe
that the whole may differ from the
sum of its parts
Attention
http://www.youtube.com/watch?v=ubNF9QNEQLA
Look at the plus sign in the middle, the pink/purple dots will disappear and be
replaced by a green ring.
The circles are not moving. If you look at one it remains stationary while the other
circles are moving.
Stare at the four black dots in the center of the image for 30 - 60 seconds.
Then quickly close your eyes and look at something bright (like a lamp or a window
with sunlight coming through it). You should see a white circle with an image inside it.
An Old Woman or a Young
Lady?
4) Perception
 Rules of Grouping
 Closure: The tendency to fill in missing
contours to form a complete object
We perceive these objects as a circle and a square.
http://www.exploratorium.edu/brain_explorer/jumping.html
4) Perception
 Proximity: The closer objects are
to one another, the more likely they
are to be perceived as belonging
together
We perceive the picture figures below as one group of 2 circles, one
single circle and another group of 2 circles.
Can you come up with examples of proximity as it relates to real life?
4) Perception
 Similarity: Similar elements are perceived
to be part of a group.

For instance, students wearing the same school colors
at a stadium will be perceived as belonging together
even if they are not seated close together
X
X
X
X
O
O
O
O
X
X
X
X
O
O
O
O
We see two columns of Xs and two columns of Os not four rows of XOXO
4) Perception
 Continuity: Sensations that appear to
create a continuous form are perceived
as belonging together
4) Perception
4) Perception
 Common Fate: Sets of objects that
move in the same direction at the same
speed are perceived together
 Examples:
A flock of birds flying in a V
formation, though separated in space,
will be perceived as a group
4) Perception
 Stroboscopic Motion: the illusion of
movement produced by showing the rapid
progression of images or objects that are
not moving at all
http://www.youtube.com/watch?v=gAvTTlXyzmE&feature=related
4) Perception
 Depth Perception: The perception of
distance, allowing us to experience the
world in three dimensions.
 Monocular
Depth cues
 Binocular Depth cues
4) Perception
 Monocular Depth cues: Depth cues
requiring the use on only one eye
 Linear Perspective
 Relative Size
 Reduced Clarity
 Interposition/Overlapping
 Texture Gradient
 Relative Height
4) Perception
 Linear Perspective: The closer
together two converging lines are, the
greater the perceived distance
4) Perception
 Relative Size: If two objects are
assumed to be the same size, the
object producing a larger image on the
retina is perceived as closer than the
one producing a smaller images
4) Perception
 Reduced Clarity: Faraway objects
seem less clear and less detailed
4) Perception
 Interposition/Overlapping: Closer
objects block the view of objects farther
away
4) Perception
 Texture Gradient: A graduated
change in the texture, or “grain” of the
visual field. Texture appears finer as
distance increases and coarser as the
distance decreases.
4) Perception
 Relative height: More distant objects
are usually higher in the visual field than
those nearby
4) Perception
 Retinal Disparity: A depth cue
based on the difference between the
retinal images received by each eye
 Closer
objects have
more retinal disparity
than objects farther
4) Perception
 As retinal disparity increases, perceived
distance _________________.
 As retinal disparity decreases, perceived
distance _________________.
4) Perception
 Convergence: A depth cue resulting
from rotation of the eyes so that the
image of an object can be projected on
each retina. The rotating of the eyes
causes feelings of tension in the eye
muscle. This tension is stronger when
objects are closer
4) Perception
 Perceptual Constancy: The
perception that objects retain the
same size, shape, color, and other
properties despite changes in their
retinal image