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CHAPTER 4
Sensation
LESSONS
4.1 Basic Principles of Sensation
4.2 Vision
4.3 Hearing and Your Other Senses
PSYCHOLOGY
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Chapter 4 Slide 1
LESSON 4.1
Basic Principles of Sensation
OBJECTIVES
 Explain the concepts of sensory thresholds and
compare the different theories.
 Describe sensory adaptation.
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Chapter 4 Slide 2
Sensory Thresholds
Sensation is the process that detects
stimuli from your body and environment.
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Chapter 4 Slide 3
Table 4-1
The Stimuli and Sensory Receptors for
Each Primary Sense
Sense
Stimulus
Sensory Receptors
Vision
Light waves
Light-sensitive rods and cones in
the retina of the eye
Hearing
Sound waves
Pressure-sensitive hair cells in the
cochlea of the inner ear
Taste
Molecules dissolved Taste cells in the taste buds of the
in fluid on the tongue tongue
Smell
Molecules dissolved
in fluid in the nose
Sensitive ends of olfactory (smell)
neurons
Touch
Pressure on the skin
Sensitive ends of touch neurons
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Chapter 4 Slide 4
Absolute Threshold
Psychophysics is the study of how
physical stimuli are translated into
psychological experience.
Absolute threshold is the weakest
amount of a given stimulus that a person
can detect half of the time.
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Chapter 4 Slide 5
Table 4-2
Examples Of Absolute Thresholds
Stimulus
Absolute Threshold
Vision
A candle seen at 30 miles on a dark, clear
night
Hearing
The tick of a watch at 20 feet under quiet
conditions
Taste
One teaspoon of sugar in 2 gallons of water
Smell
One drop of perfume diffused into a threeroom apartment
Touch
The wing of a fly falling on your cheek from a
distance of 0.5 inch
Source: Adapted from Galanter, 1962.
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Chapter 4 Slide 6
Signal-Detection Theory
Signal-detection theory states that
detecting a stimulus is influenced by a
person’s decision-making strategy.
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Chapter 4 Slide 7
Difference Threshold
Difference threshold is the smallest
difference between two stimuli that can
be detected half of the time.
Weber’s law is the principle that to be
noticed as different, two stimuli must
differ by a constant minimum
percentage rather than by a constant
amount.
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Chapter 4 Slide 8
Sensory Adaptation
Sensory adaptation is the tendency for
sensory receptors to decrease in
response to stimuli that continue at the
same level.
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Chapter 4 Slide 9
LESSON 4.2
Vision
OBJECTIVES
 Identify and illustrate the structures of the eye
that are responsible for vision.
 Describe the way the brain perceives color.
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Chapter 4 Slide 10
Figure 4-1
The Electromagnetic Spectrum
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Chapter 4 Slide 11
Structures of the Human Eye
 The pupil is an opening in the iris that allows light to
enter the eye.
 The iris is a ring of muscles that range in color from
light blue to dark brown.
 The lens is a clear, elastic, disc-shaped structure that
refocuses light.
 The retina is the light-sensitive surface at the back of
the eye.
 The optic nerve carries information from the retina to
the brain.
 The blind spot is the area on the retina where the
optic nerve leaves the eye and that contains no
receptor cells.
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Chapter 4 Slide 12
Figure 4-2
Major Structures Of The Human Eye
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Chapter 4 Slide 13
Video
Anatomy of the Eye (Virtual Reality)
Videos are located on the Instructor’s
Resource CD in the Videos folder.
Filename: AnatomyEyeVR
Running time: variable
This video is activated by moving the
mouse over the video screen to explore the
anatomy of the eye.
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Chapter 4 Slide 14
Figure 4-3
How Light Travels through the Eye
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Chapter 4 Slide 15
Videos
Transmission of Light through the Eye
Videos are located on the Instructor’s
Resource CD in the Videos folder.
Filename: LightThroughEye
Running time: 28 seconds
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Chapter 4 Slide 16
Color Vision
 All the colors you see are red, blue, and
green, or a mixture of these three.
 The color is in your visual system.
 An object appears as a particular color
because it absorbs or reflects certain
wavelengths of light.
 Colors are created by the cones in your eye
responding to wavelengths and sending
neural signals to your brain, which then
creates the colors you see.
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Chapter 4 Slide 17
Color Blindness
Color blindness is a deficiency in the
ability to distinguish among colors.
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Chapter 4 Slide 18
Figure 4-4
Test for Color Blindness
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Chapter 4 Slide 19
LESSON 4.3
Hearing and Your Other Senses
OBJECTIVES
 Explain and illustrate the human auditory
system and the structure of the ear.
 Describe the senses of smell, taste, touch, and
body position and movement.
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Chapter 4 Slide 20
The Auditory System
The auditory system controls your sense
of hearing.
Hearing begins with sound waves—
vibrations in air, water, or solid material.
The number of sound waves that pass
through a given point in one second is
called the sound’s frequency.
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Chapter 4 Slide 21
The Auditory System—Pitch
When your sensory system experiences
the physical sensation of frequency, you
also have the psychological experience
of pitch.
High-pitched sounds are high frequencies
Low-pitched sounds are low frequencies.
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Chapter 4 Slide 22
The Auditory System—Amplitude
Loudness of sound is a psychological
experience that corresponds to the
height of a sound wave, called
amplitude.
Amplitude is measured in decibels (dB).
The greater the amplitude, the higher the
decibels, and the louder the sound.
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Chapter 4 Slide 23
Table 4-3
Decibel Level of Some Common Sounds
Decibels
Source
Exposure Danger
180
Space shuttle launch
Hearing loss certain within 150
feet of launch pad
140
Jet aircraft motor
Any exposure dangerous
120
Sandblaster, thunderclap
Immediate danger
100
Heavy auto traffic, lawn
mower
2 hours
60
Normal conversation
No danger
40
Quiet office
No danger
30
Quiet library
No danger
20
Soft whisper
No danger
0
Minimal detectable sound
No danger
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Chapter 4 Slide 24
The Ear
The ear is divided into three major parts:
The outer ear is the part you see.
The eardrum is a thin, flexible membrane
that vibrates in sequence with sound
waves.
The cochlea is the coiled, fluid-filled tube in
the inner ear that contains hair-like auditory
receptors.
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Chapter 4 Slide 25
Figure 4-5
The Human Ear
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Chapter 4 Slide 26
Hearing Loss
There are two types of hearing loss:
Conduction hearing loss
Sensorineural hearing loss
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Chapter 4 Slide 27
Conduction Hearing Loss
 Occurs when there are physical problems
sending sound waves through the outer or
middle ear
 Often involves a punctured eardrum or
damage to any of the bones in the middle ear
 Hearing aids
 Common treatment for conduction hearing
 Tiny instruments worn just inside the outer ear
 Change sound waves into amplified vibrations and
send them to the inner ear
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Chapter 4 Slide 28
Sensorineural Hearing Loss
 More common than conductive hearing loss
 Involves nerve problems in the inner ear
 Often occurs because hair cells in the cochlea
are damaged either by disease, injury, or
aging
 Cochlear implant
 Only means of restoring hearing
 Miniature electronic device surgically placed into
cochlea
 Changes sound waves into electrical signals
 Best candidates—young children born with hearing
loss
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Chapter 4 Slide 29
Smell
 Olfactory nerve transmits neural impulses
containing smell information from the nose to
the brain.
 The stimuli for smell are airborne molecules.
 These molecules enter your nasal passages and
reach tiny receptor cells at the top of the nasal
cavity.
 These receptor cells then transmit neural impulses
containing smell information through the olfactory
nerve to the brain.
 Once your brain has processed these neural
signals, you experience the aroma or odor.
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Chapter 4 Slide 30
Figure 4-6
The Olfactory System
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Chapter 4 Slide 31
Taste
 Taste buds are sensory receptor organs that
contain the receptor cells for taste.
 Taste occurs when receptor cells in your
mouth and throat trigger neural impulses to
the brain.
 About 50 to 150 of these receptor cells are
contained in each of the 10,000 taste buds
that are located mainly on the tongue.
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Chapter 4 Slide 32
Taste Sensations
 Four most familiar taste sensations:
 Sweetness (mostly sugars)
 Sourness (mostly acids)
 Saltiness (mostly salts)
 Bitterness (mainly chemicals that have no food
value or are toxic)
 Most taste experiences are complex and
result from the combined effects of receptor
cells in the mouth and nose, which produce
the different flavors you experience.
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Chapter 4 Slide 33
Figure 4-7
The Tongue Map Myth
Myth: Different areas of
the tongue are more
sensitive to one of the
four primary tastes.
Fact: All your taste buds
detect all taste qualities.
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Chapter 4 Slide 34
The Skin Senses
Skin defines boundaries with the
environment.
Skin is your largest sensory organ.
The sense of touch is actually a
combination of three skin senses:
Pressure
Temperature
Pain
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Chapter 4 Slide 35
Pressure
The stimulus for pressure is physical
pressure on the skin.
The entire body is sensitive to pressure.
Some areas have more receptors so are
more sensitive.
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Chapter 4 Slide 36
Temperature
Temperature sensations depend on
which type of receptor is stimulated.
Whether more warm or cold receptors
are stimulated depends on the
difference between your skin
temperature and the temperature you
are feeling.
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Chapter 4 Slide 37
Pain
 Pain serves as a warning system that signals
danger and the risk of injury.
 Pain can also force people to cope
appropriately with an injury.
 The most widely accepted theory of pain is
gate-control theory.
 Gate-control theory describes how pain
signals open a neurological “pain gate” in the
spinal cord and how other touch signals close
the gate.
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Chapter 4 Slide 38
Body Position and Movement
Kinesthetic sense provides information
about the movement and location of
different parts of your body.
Vestibular sense provides information
on the position of your body by sensing
gravity and motion.
Equilibrium is another name for
vestibular sense.
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Chapter 4 Slide 39
Chapter 4
Clicker Questions
1. Which refers to nerve cells firing less
frequently after high levels of
stimulation?
a. critical thinking
b. environmental threshold
c. absolute threshold
d. sensory adaptation
PSYCHOLOGY
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Chapter 4 Slide 40
Chapter 4
Clicker Questions
2. The major contribution of the signaldetection theory was the establishment
of specific absolute thresholds for all
senses.
a. True
b. False
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Chapter 4 Slide 41
Chapter 4
Clicker Questions
3. Which is a ring of muscles that range
in color from light blue to dark brown?
a. pupil
b. iris
c. lens
d. retina
PSYCHOLOGY
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Chapter 4 Slide 42
Chapter 4
Clicker Questions
4. Loudness of a sound corresponds to
the height of a sound wave called
a. amplitude
b. pitch
c. frequency
d. timbre
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Chapter 4 Slide 43
Chapter 4
Clicker Questions
5. What is the term for the senses that
detect body position and movement?
a. olfactory
b. proprioceptive
c. sensorineural
d. auditory
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Chapter 4 Slide 44