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CHAPTER 5
SENSATION AND PERCEPTION
List the five senses below
1.
2.
3.
4.
5.
Sensation and Perception:
The Basics
 Sensation: Raw information that
comes from the senses
What is this?
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
Sensation and Perception:
The Basics
Bottom-Up Processing
Informational Processing that analyzes
the raw stimuli entering through the many
sensory systems and works up the brain
Top-Down Processing
Information Processing that draws on
expectations and experiences to interpret
incoming sensory information. It is
guided by higher-level mental processes
Sensing the World: Some Basic
Principles
 Psychophysics:
the study of relationships between the
physical characteristics of stimuli, (such
as their intensity), and our psychological
experience of them
Sensing the World: Some Basic
Principles
 Absolute Threshold:
The
weakest amount of stimulation
needed to detect a stimulus
50% of the time
Sensing the World: Some Basic
Principles
 Examples of Absolute Thresholds





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)
Sensing the World: Some Basic
Principles
 Absolute Threshold are different for
people due to psychological and
biological factors.
 What
are some examples?
Sensing the World: Some Basic
Principles
 Signal-Detection Theory: A theory
that predicts how and when we detect
the presence of a faint stimulus (signal)
amid background stimulation (noise).
This theory assumes there is no single
absolute threshold and that detection
depends partly on a person’s
experience, expectations, motivation,
and level of fatigue.
1.) Sensation and Perception:
The Basics
 Our ability to distinguish between sensory
stimuli takes into account:




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)
Sensing the World: Some Basic
Principles
 Subliminal Stimulation
 Subliminal: below threshold stimuli
Can we detect subliminal stimuli?
 Can subliminal messages manipulate
our behavior?

Sensing the World: Some Basic
Principles
 Priming:
the activation, often unconsciously,
or certain associations, thus
predisposing one’s perception,
memory, or response
Sensing the World: Some Basic
Principles
 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
 What
jobs would require a person
to have a small difference
threshold?
Sensing the World: Some Basic
Principles
 Weber’s Law:
Sensory thresholds for detecting differences
(JND) are a roughly constant proportion of
the size of the original stimulus
Difference thresholds grow with the
magnitude of the stimulus
Sensing the World: Some Basic
Principles
 As we get older, our JND increases
Sensing the World: Some Basic
Principles
 Fechner’s Law
Constant increases in physical energy will
produce smaller increases in perceived
magnitude
Sensing the World: Some Basic
Principles
 Sensory Adaptation: our
diminishing sensitivity to an
unchanging stimulus
Why does sensory adaptation occur?
Sensing the World: Some Basic
Principles
 Sensory Adaptation
Why does sensory adaptation occur?
Sensory adaptation allows us to
detect potentially important changes
in our surroundings while ignoring
unchanging aspects of them.
Example?
Sensing the World: Some Basic
Principles
 We will never completely adapt to
extremely intense sensations such
as severe pain or freezing cold.
 This is adaptive because to ignore
such stimuli might be harmful or
even fatal.
Vision
Transduction:
conversion of one form
of energy into another. In sensation, the
transforming of stimulus energies, such as
sights, sounds, and smells, into neural
impulses our brain can interpret

Example: the ear receives sound energy and
transduces it into neural activity that people
recognize as voices
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.
Vision
 Stimulus Energy: Light Energy


Light is described in wavelengths
Can we see all wavelengths of light?

No
Vision
 The Stimulus Input: Light Energy
 Wavelength: the distance from one
wave peak to the next. Wavelength
determines hue/color
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
Vision
 The Stimulus Input: Light Energy
 Amplitude: the height of a wave
from peak to trough. It determines the
intensity (or brightness of color)
The Eye
 The Eye
The eye works much like a camera
does
The Eye
 Parts of the Eye
The Eye
Cornea:
Covers and protects the eye. It is through this structure that
The Eye
 Parts of the eye
Pupil:
An opening in
the eye just behind the
cornea, through which
light passes. The size of
this opening can be
affected by the amount of
light present and by
emotions
2.) Vision
 Parts of the Eye
Iris: The part of the
eye that gives its color and
adjusts the amount of light
entering it
The Eye
Parts of the eye
Lens: The transparent
structure behind the
pupil that focuses light
onto the retina
The Eye
 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
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Cornea
Pupil
Lens
Retina
The Eye
 The Blind Spot:
The point at which the optic nerve
leaves the eye creating “blind” spot
because no receptor cells are
located there
The Eye
 Accommodation:
 The process by which the eye’s lens
changes shape to focus near or far
objects on the retina
The Eye
 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
The Eye
 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)
The Eye
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
The Retina
 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
The Retina
 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)
The Retina
The Retina
 Optic Nerve
 The
nerve that carries neural
impulses from the eye to the brain
Visual Information Processing
 Feature Detection

We process information at progressively
more abstract levels. The information form
the retina’s 130 million rods and cones is
received and transmitted by the million or
so ganglion cells whose axons make up
the optic nerve. When individual ganglion
cells register information in their region of
the visual field, they send signals to the
visual cortex.
Visual Information Processing
 Features Detectors

Nerve cells in the brain that respond to
specific features of the stimulus, such as
shape, angle, or movement
Parallel Processing
 Parallel Processing:

The processing of several aspects of a
problem simultaneously (color, shape, motion,
and depth); the brain’s natural mode of
information processing for many functions,
including vision (simplistically put…doing
several things at once)
Parallel Processing
 Blind sight:

The capacity of some individuals with
blindness in parts or all of the visual field to
detect and localize visual stimuli presented
within the blind field region. However, these
visual capacities are not accompanied by
awareness. They have been demonstrated
only in experimental conditions, when
participants are forced to guess. Blind sight
therefore does not help individuals to
compensate for their loss of vision
Color Vision
 Young-Helmholtz Trichromatic Theory
 Any
color can be created by combining
light waves of the three primary colors
which are red, green, and blue
Color Vision
 Young-Helmholtz Trichromatic Theory
 The
human eye has three types of
receptors (cones) each of which is most
sensitive to one of the primary colors.
When combined in differing amounts, they
can produce the perception of any color
www.exploratorium.edu/exhibits/f_exhibits.html
Color Vision
 Short wavelength cones

Respond most to blue
 Medium wavelength cones

Are most sensitive to green
 Long wavelength cones

Respond best to red
Color Vision
 Opponent-Process Theory:
 This
theory states that opposing retinal
processes enable color vision.
 These opposing processes are:
 Red-green
Santa Claus

Yellow-blue
at a Marquette game

White-black
reading a newspaper
Color Vision
 Opponent-Process Theory:
 There are three different kinds of color processing
neural mechanisms in the visual system. These
neurons work on an “on-off’ system

If the red-green mechanisms is activated by light in
the red wavelengths it will be shut down by lights in
the green range. Others are turned on by green
and off by red. So if you detect red at a particular
point in the retina, you cannot simultaneously
detect the opposing color (green) at the same point;
you therefore cannot see a greenish red
Color Vision
 Opponent-Process Theory:

If both members of a pair are stimulated
equally, they cancel each other out and this
leaves only gray.

Member from non-opponent pairs may interact
and be stimulated at the same time result in
colors such as yellow-red or blue green

The black-white system respond to differences
in brightness levels
Color Vision
 Support for the opponent-process theory

Complementary colors: You can’t mix
yellow/blue or red/green to get intermediate
colors, simultaneous presentation of both colors
typically produce white or gray tones because
they are complementary colors. The opponentprocess theory explains this by saying that you
cannot signal red and green at the same time.
In contrast, you get orange when the red and
yellow neural mechanisms are simultaneously
stimulated
Color Vision
 Support for the opponent-process theory

Color after image: If you stare at a color for a
long time you will see a visual image that
persists after it is removed; the color of the
afterimage is the complement. Why? If you
stare at something green for a long time you
fatigue the green receptors. Then when you
state at something white (which contains all
colors) the green receptors, which are fatigued,
do not fire, only the red receptors fire normally
www.exploratorium.edu/exhibits/f_exhibits.html
Color Vision
 Support for the opponent-process theory

Color Blindness: In partially color blind
people they usually
have trouble with
red/green or
yellow/blue which
are opponent pairs
Color Vision
 Color Blindness: People who do not have
normal color vision are said to be color blind
Normal Vision
Color Blind Vision
Color 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
Color Vision
 Color Blindness
 More
men than woman are color
blind because it is a trait carried
on the X chromosome
Color Vision
 Which theory of color vision is correct?

They both are. Both theories are
needed to account for the complexity of
visual sensations of color
Color
Vision
Color
Vision
=
+
=
Trichromatic
Theory
+
Opponent Process
Theory
Color Vision
 There are two steps in color processing
1.
2.
The cones in the retina respond to and
encode color in terms of red, green, and blue.
This supports the Trichromatic Theory, which
describes the visual processing in the retina
The ganglion cells respond to and encode
color in terms of opposing pairs en route to the
visual cortex. This supports the OpponentProcess Theory, which describes color vision
at higher levels within the brain
Path of Light as it enters the eye
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Color Constancy
 Color Constancy: Perceiving familiar
objects as having consistent color, even if
changing illumination alters the wave-length
reflected by the object. If it weren’t for
perceptual constancy the world would seem
ever-changing and chaotic.
Hearing
 Audition

The sense of hearing
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
Hearing
 Amplitude
The height of a sound wave
 Amplitude determines how loud a sound is

Hearing
 Loudness:
 Measured in units called decibels (dB)
 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
 Continued noise at upper limits (85dB) can
cause permanent hearing loss
Hearing
Hearing
 Frequency
 the
complete wavelengths that pass
by a given point each second
Hearing
 Frequency


Frequency is measured in Hertz units (Hz)=
number of cycles per second
Wavelengh and frequency are related. The
longer the wavelength, the lower the
frequency, and vice versa
Hearing
 Frequency and Pitch
 Frequency
determines pitch
 High frequency/short wavelength= high
pitch

Examples?
 Low
frequency/long wavelength=low
pitch
Examples?
We hear sound best that have the frequencies
within the range of the human voice


Hearing
 “Oh Grandma, what big ears you
have.”
 “The better to hear you with my
dear.”
 True or false?
Hearing
 Parts of the Ear
Pinna:
the ear flap
Hearing
Auditory Ear Canal
The hollow tube that
conducts sound
through the external
ear, from the pinna
to the ear drum
Hearing
Ear Drum:
The Ear Drum is a piece of skin stretched over the entrance to
the ear, it separates the external ear from the middle ear and
serves to transform the pressure waves of sounds into
mechanical vibrations of the bone of the middle ear.
Hearing
Middle Ear (Hammer, Anvil, Stirrup)
The hammer, anvil and stirrup are the auditory ossicles that
transmit sound vibrations from the tympanic membrane to the oval
window of the inner ear. The ossicles allow efficient transmission
of sound from air to the fluid-filled cochlea
Hearing
 Middle Ear (Malleus, Incus, Stapes)
hammer
anvil
stirrup
Hearing
Oval Window: The membrane in the wall of
the cochlea to which the stapes is attached.
By the time the sound has reached the oval
window, it is many times stronger than when it
first struck the eardrum.
Oval Window
Hearing
 Semicircular Canals
Semicircular Canals
A set of three looped tubular channels in the inner ear that detect
movements of the head and provide the sense of equilibrium that is
essential for maintaining balance. They are oriented roughly at right angles
to each other, and can therefore monitor movements in each of three
different planes.
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
Hearing
Basilar Membrane: the floor of the fluid
filled duct that runs through the cochlea. This
organ contains the hair cells called cilia. The
movement of the fluid within the cochlea causes
the cilia to bend and as they bend, nerve
impulses are sent via the auditory nerve to the
brain
Hearing
Auditory Nerve
The Auditory Nerve is a bundle of nerves that carry stimuli
from the hair cells of the cochlea to the temporal lobe of the
brain where auditory processing occurs
Three Sections of the Ear
OUTER EAR
MIDDLE EAR
INNER EAR
___________the
sound. Sound
travels by means of
___________the
sound by means of
___________
sound into neural
energy by means of
Consists of:
Consists of:
Consists of:
Hearing
 How do we perceive pitch?
 Place Theory: This theory links the
pitch we hear with the place where
the cochlea’s membrane is
stimulated.
Hearing
 How do we perceive pitch?
 Place Theory

High Frequency waves (high pitched
sounds) trigger activity mostly near the
beginning/base of the cochlea’s
membrane, near the oval window
Hearing
 How do we perceive pitch?
 Place Theory

Middle Frequency waves (medium
pitched sounds) trigger activity at the
apex of the cochlea
Hearing
 How do we perceive pitch?
 Place Theory

The place theory describes how we
hear high frequency/high pitched
sounds but doesn’t do a great job of
explaining how we hear low pitched
sounds
Hearing
 Frequency Theory: This 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
 The
frequency theory describes best
how we hear low frequency/low pitched
sounds
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
Hearing
 Locating Sound:
It is difficult to locate sounds that
are directly in front, behind, or on
top of our ears. Why?
Because the sound reaches both of
our ears at the same time and with
the same intensity.
Hearing
 Deafness
 About
2 million Americans are
deaf
 There are two basic types of
deafness
Conductive deafness
 Sensorineural deafness (nerve
deafness)

Hearing
 Conductive Deafness
 Occurs due to damage to the middle
ear (damage to the mechanical
system that conducts sound waves to
the cochlea)
 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
Hearing
 Sensorineural Deafness (Nerve
Deafness)
 Occurs
due to damage to the inner ear
(the cochlea’s receptor cells or to the
auditory nerves)
 Could result from:
Disease
 Prolonged Exposure to very loud sounds
 Biological changes associated with age

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
Hearing
 Cochlear Implant: A device for converting
sounds into electrical signals and stimulating
the auditory nerve through electrodes
threaded into the cochlea
(The first implant was done in 1980)
Hearing
 Controversy:
One group supports the use of cochlear implants
to medically "repair" deafness in children with a
sensorineural hearing loss while the other
believes the children's natural condition should be
emphasized. Those who support cochlear
implants believe that normalization is the key to
success for deaf children. On the other side, the
Deaf community and others opposed to cochlear
implants feel that deafness should be looked at
as a cultural identity, not a disability
Hearing
 Cochlear Implants
 Sensory

Compensation
Some also argue that sensory
compensation, which enhances other
senses, gives deaf people an
advantage that the hearing do not
have
Other Important Senses
 Touch: our sense of touch is a mix of at least
four distinct skin senses




pressure
warmth
cold
pain
These four senses combine to produce other
sensations, such as “hot”
Other Important Senses
 Touch
 The sense of touch codes information
about two aspects of an object in
contact with our skin
Intensity: how heavy it is (coded by the
firing rate of neurons. The higher the
rate of firing, the heavier the objects)
 Location: where the touch is

Other Important Senses
 Pain: There is not one type of stimulus
that triggers pain, and there are no
special receptors for pain. However,
pain is an alarm system that draws out
attention to some physical problem.
Other Important Senses
 Pain
 There are two types of nerve fibers
that carry pain signals from the skin to
the spinal cord
A-delta fibers: carry sharp, pricking pain
sensations. They are myelinated
 C fibers: carry chronic, dull aches and
burning sensations

Other Important Senses
 Biological, Psychological, and Social-
Cultural Influences on Pain

The biopsychological approach views pain not
only as product of biological influences but
also as a result of psychological influences
such as the situation and our past experience
and social influences such as cultural
expectations and the presence of observers
Other Important Senses
 Gate-Control Theory: This theory states
that there is a “gate” in the spinal cord that either
lets pain impulses travel upward to the brain or
blocks their progress. The major parts of this
theory are incorrect. However, there is some
evidence that natural mechanisms can block
pain sensation by coming in to the spinal cord at
the same time as the pain gets there and “taking
over” the pathways that the pain impulses would
have used.
Other Important Senses
 Pain Control

Pain is controlled through a combination of
medical and psychological treatments.
Other Important Senses
 Taste: the sense of taste is called gustation

Taste (a chemical sense) is composed of






Sweet
Sour
Salty
Bitter
Umami (meat, fish, some vegetables, and
cheeses)
And aromas that interact with information from
taste buds
Other Important Senses
This theory has largely
been debunked
Babies seem to be born
disliking bitter tastes
Other Important Senses
 These taste buds on the top and sides of the
tongue and in the back and roof of the mouth
contain taste receptor cells. These cells send
information to an area of the temporal lobe
near the area where olfactory information is
received.
 Taste receptors replace themselves every
week
Other Important Senses
 Supertasters: (25%)
 Have
more papillae than the average
person
Other Important Senses
 Sensory Interaction:
 We taste with more than just our taste buds.
Our sense of smell and vision are also
involved in our sense of taste.
 Other facts about taste
 Food deprivation or salt deficiency makes
sweet or salty foods taste better
 Flavor is affected by tactile properties

Warm food= sweeter
Other Important Senses
 Smell: The sense of smell is called
olfaction
Other Important Senses
 Kinesthesia
Other Important Senses
 Vestibular Sense