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Chapter 5
Sensation
James A. McCubbin, PhD
Clemson University
Worth Publishers
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
Sensation and Perception

Paris
in the
the spring
Sensation and Perception
Sense
Input
Perception
Sight
colors/shapes object/event
Hearing
sound/noise words/music
Touch
pressure/temp
feel of object
Taste sour/salty/bitter/sweet flavor
Smell spicy/resinous/burned
odor

rotten/fruity/flowery
Perception
Physiological variables:
Receptors available
Receptor limits
Receptor abnormalities
Sensory adaptation- diminished sensitivity as
a consequence of constant stimulation
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.
Perception
Psychological variables
Interests
Motivation
Expectancy set
Emotion
Attitudes
Values
Gestaltists
Gestalt means “whole” in German. The
Gestaltists believed that people look to
form patterns and complete whole images
when they perceive things around them
Sensation and Perception
Sensation
 Our
sensory
and
perceptual
processes
work
together to
help us
sort out
complex
processes
Sensation and Perception
Perceptually Impaired
Iti soft ennotre alized howcom plexT
heproces sofrea ding is. Afe w sim plerear
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used!
Top-Down Processing
Information processing guided by higher-level
mental processes as we construct perceptions,
drawing on our experience and expectations.
THE CHT
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.”
Sensation- Basic
Principles
 Psychophysics
 study of the relationship between
physical characteristics of stimuli and
our psychological experience of them
 Light- brightness
 Sound- volume
 Pressure- weight
 Taste- sweetness
Sensation- Thresholds
 Absolute Threshold
 minimum stimulation needed to detect a
particular stimulus 50% of the time
 Difference Threshold
 minimum difference between two stimuli
required for detection 50% of the time
 just noticeable difference (JND)
Sensation- Thresholds
 Signal Detection Theory
 predicts how and when we detect the presence
of a faint stimulus (signal) amid background
stimulation (noise)
 assumes that there is no single absolute
threshold
 detection depends partly on person’s
 experience
 expectations
 motivation
 level of fatigue
Sensation- Thresholds
100
Percentage
of correct
detections
 Subliminal
75
50
Subliminal
stimuli
25
0
Low
Absolute
threshold
Intensity of stimulus
Medium
 When stimuli are
below one’s
absolute
threshold for
conscious
awareness
Sensation- Thresholds
 Weber’s Law- to perceive as different,
two stimuli must differ by a constant
minimum percentage




light intensity- 8%
weight- 2%
tone frequency- 0.3%
Ex. A three way bulb
Weber’s Law
Vision
Vision
 Pupil- adjustable opening in the
center of the eye
 Iris- a ring of muscle that forms the
colored portion of the eye around the
pupil and controls the size of the
pupil opening
 Lens- transparent structure behind
pupil that changes shape to focus
images on the retina
Retina’s Reaction
to Light
 Optic nerve- nerve that carries neural
impulses from the eye to the brain
 Blind Spot- point at which the optic nerve
leaves the eye, creating a “blind spot”
because there are no receptor cells located
there
 Fovea- central point in the retina, around
which the eye’s cones cluster
Blind Spot
Vision- Stabilized
Images on the Retina
Vision
 Transduction
 conversion of one form of energy to
another
 in sensation, transforming of stimulus
energies into neural impulses
 Wavelength
 the distance from the peak of one
wave to the peak of the next
Vision
 Accommodation- the process by which
the eye’s lens changes shape to help
focus near or far objects on the retina
 Retina- the light-sensitive inner surface of
the eye, containing receptor rods and
cones plus layers of neurons that begin
the processing of visual information
Vision
 Acuity- the sharpness of vision
 Nearsightedness- condition in which
nearby objects are seen more clearly than
distant objects because distant objects in
front of retina
 Farsightedness- condition in which
faraway objects are seen more clearly
than near objects because the image of
near objects is focused behind retina
Vision
 Farsighted
 Vision
Nearsighted
Vision
Normal
Vision
Vision
 Hue
 dimension of color determined by
wavelength of light
 Intensity
 amount of energy in a wave
determined by amplitude
 brightness
 loudness
The spectrum of
electromagnetic
energy
Vision- Physical
Properties of Waves
Short wavelength=high frequency
(bluish colors, high-pitched sounds)
Great amplitude
(bright colors, loud sounds)
Long wavelength=low frequency
(reddish colors, low-pitched sounds)
Small amplitude
(dull colors, soft sounds)
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
Photoreceptors
E.R. Lewis, Y.Y. Zeevi, F.S Werblin, 1969
Color-Deficient Vision
 People who suffer
red-green
blindness have
trouble perceiving
the number within
the design
Visual Information
Processing
 Trichromatic (three color) Theory
 Young and Helmholtz
 three different retinal color receptors
 red
 green
 blue
Afterimages
Opponent ProcessAfterimage Effect
Visual Information
Processing
Opponent-Process Theory- opposing retinal
processes enable color vision
“ON”
“OFF”
red
green
green
red
blue
yellow
yellow
blue
black
white
white
black
Pathways from the Eyes
to the Visual Cortex
Visual Information
Processing
 Color Constancy
 Perceiving familiar objects as having
consistent color, even if changing
illumination alters the wavelengths
reflected by the object
Feature Detection
Ross Kinnaird/ Allsport/ Getty Images
Nerve cells in the visual cortex respond to
specific features, such as edges, angles, and
movement.
How the Brain
Perceives
Illusory Contours
Visual Information
Processing
 Parallel Processing
 simultaneous processing of several
aspects of a problem simultaneously
The Ear
Dr. Fred Hossler/ Visuals Unlimited
The Ear
Pinna- the external funnel shaped portion
of the ear
External Auditory Canal -directs sound
waves to the eardrum
Eardrum- thin piece of skin that vibrates
to incoming sound
Audition- The Ear
 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, contining the cochlea,
semicircular canals, and vestibular sacs
 Cochlea
 coiled, bony, fluid-filled tube in the inner ear through
which contains the cilia receptors for hearing on the
basilar membrane.
Audition
 Audition
 the sense of hearing
 Frequency
 the number of complete wavelengths
that pass a point in a given time
 Pitch (measured in Hertz)
 a tone’s highness or lowness
 depends on frequency
Audition
 Place Theory
 the theory that links the pitch we hear with
the place where the cochlea’s membrane is
stimulated
 Frequency Theory
 the theory that the rate of nerve impulses
traveling up the auditory nerve matches the
frequency of a tone, thus enabling us to
sense its pitch
How We Locate
Sounds
Location with Sound
Doppler Shift- as something approaches
the pitch is higher and as it recedes the
pitch is lower. Ex. The train coming into
the station.
The Intensity of Some
Common Sounds
Audition
 Older people tend to hear low
frequencies well but suffer hearing loss
for high frequencies
Amplitude required for
perception relative to
20-29 year-old group
1
time
10
times
100
times
1000
times
32
64
128
256
512
1024 2048 4096
8192 16384
Frequency of tone in waves per second
Low
Pitch
High
Deafness
Tinnitus- ringing in the ears when there is
no external auditory stimulation caused by
exposure to loud noise and represents
damage to the auditory nerve.
Deafness
 Conduction Hearing Loss
 hearing loss caused by damage to the
mechanical system that conducts sound
waves to the cochlea
 Nerve Hearing Loss
 hearing loss caused by damage to the
cochlea’s receptor cells or to the auditory
nerve
Deafness
Choices in adjusting to hearing loss:
Lip reading- family members and others must
be careful to insure that their lips can be seen at
all times during conversation
American Sign Language- a set of symbols that
represent words or phrases
Cochlear Implant- an electrode is placed in the
cochlea that artificially sends sound to the
temporal lobe.
Touch
 Skin Sensations
 pressure
 only skin sensation
with identifiable
receptors most on
the hands and back
of neck EX back vs.
face 2pt. threshold
 warmth
 cold
 pain
Touch
Bruce Ayers/ Stone/ Getty Images
The sense of touch is a mix of four distinct skin
senses—pressure, warmth, cold, and pain.
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
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.
AP Photo/ Stephen Morton
Ashley Blocker (right) feels neither pain
nor extreme hot or cold.
Biopsychosocial Influences
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
Pain
 Gate-Control Theory
 theory that the spinal cord contains a
neurological “gate” that blocks pain
signals or allows them to pass on to the
brain
 “gate” opened by the activity of pain
signals traveling up small nerve fibers
 “gate” closed by activity in larger fibers
or by information coming from the brain
Pain
State of mind can affect intensity of pain:
WWI soldiers were relieved to be
wounded to escape the terror of the
battlefield.
Athletes “play with pain” due to
endorphins and realize the next day how
they have injured themselves.
Pain tolerance
Touch
There seems to a biological need for touch.
Babies who are not touched suffer from “failure
to thrive” which means they do not grow and
eventually die.
Premature babies in a study by Tiffany Field
wear proven to benefit from daily massage and
went home from the hospital sooner.
In adults massage lowers cortisol levels and
reduces the effect of stress.
People in this culture have been “touch
starved”.
Body Position and
Movement
 Kinesthesis
 the system for sensing the position and
movement of individual body parts
 Proprioception-sense of the movement of
muscles and tendons (body parts) in space.
 Vestibular Sense
 the sense of body movement and position
 including the sense of balance
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
(Fresh
Chicken)
Taste
Taste Receptors
Taste
 Taste Sensations




sweet
sour
salty
Bitter
 Some taste sensations are genetically programmed, such as sweet,
and finding bitter and sour foods unpleasant
 A study of babies had sweet eliciting smiles, lip smacking, and sour
eliciting protrusion of tongue
 These reactions make good evolutionary sense
 Animals tend to be neophobic, and human children are reluctant to
try new things
 One experiment asked a group of subjects to taste two groups of
food (that were the same). When the items were accurately named
(chopped tomatoes, oatmeal, beefsteak) more willing them when
given novel names (pendula fruit, lat, langua steak)
Taste
Moisture is necessary for taste buds to
function.
Taste buds are located in the fungiform
papillae or bumps on the tongue. There
are many taste buds in each bump.
Supertasters have an extraordinary
number of taste buds and fungiform
papillae. They can always taste PROP.
Spicy food tastes very hot to supertasters
as the taste bud are linked to pain
receptors that respond to the hot oil.
Taste
Sensory interaction- taste is highly
dependent on smell. The two together
create flavor. This is evident when you
have a cold. Taste also depends on sight.
If it doesn’t look good, it doesn’t taste
good.
Chocolate increases serotonin particularly
in women and increases happiness.
Smell
Olfactory
nerve
Olfactory
bulb
Nasal
passage
Receptor cells in
olfactory membrane
Smell
Like taste, smell is a chemical sense. Odorants
enter the nasal cavity to stimulate 5 million
receptors to sense smell. Unlike taste, there are
many different forms of smell.
Age, Sex and Sense
of Smell
Number
of correct
answers
Women and young adults
have best sense of smell
4
Women
3
Men
2
0
10-19
20-29
30-39
40-49
50-59
60-69
Age Group
70-79
80-89 90-99
Smell
Theories of smell:
Lock and Key- odor molecules fit specific
receptor sites
Receptor construction- as a molecule
enters the system an appropriate receptor
is formed.
Smell
Olfactory cells are located on the cilia in
the upper portion of the nose. They are
surrounded by mucus to trap odor
molecules.
Smell is associated with memory
encoding.
 Smell declines with age
Anosmia- 2 million people have no sense
of smell. Can be the result of head trauma
or infection or cold.
Smell
Pheromones-sexual signals through
smell. Used by animals and maybe
humans. Ex. Sweaty t-shirts,
menstrual synchrony
Smell is important to taste. Ex. When
one has a cold.