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accounts well for pitch perception of frequencies above 1；000 Hz； while
frequency theory accounts well for pitch perception of frequencies below
5；000 Hz。
F。 Sound Localization
1。 Some animals； such as bats； use echolocation instead of vision to
determine distances； locations； sizes； textures； and movements of objects。
Humans lack this ability； but do use sound to determine location
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CHAPTER 4： SENSATION
through two primary mechanisms； assessment of relative timing and
relative intensity。
2。 Relative timing involves the parison of the relative times at which
ining sound reaches the ear。 For example； a sound to your right
reaches your right ear before it reaches your left ear。
3。 Relative intensity involves the parison of the relative intensity at
which ining sound reaches the ear。 The head casts a sound shadow
over the ear farthest from the sound that weakens the sound。
IV。 Your Other Senses
A。 Smell
1。 Odors first interact with receptor proteins on the membranes of tiny
hairs （olfactory cilia） in your nose
2。 As few as eight molecules of a substance can initiate a nerve impulse；
but at least 40 nerve endings must be stimulated before a substance can
be smelled。
3。 Once initiated； nerve impulses convey odor information to the olfactory
bulb； located just above the receptors and just below the frontal lobes of
the cerebrum
4。 Olfactory neurons； unlike most neurons； are constantly dying and being
replaced
5。 Although it is thought that smell developed primarily as a means of
detecting food； it can also be used for active munication by the
secretion of pheromones
6。 Pheromones are chemical substances used by a specific species to signal
sexual arousal； danger； territorial boundaries； and food sources
B。 Taste
1。 Many tastes are really smells； as the two work closely together when we
eat
2。 The surface of the tongue is covered with papillae
3。 Many papillae contain clusters of taste receptor cells called taste buds
4。 Taste buds respond best to one of four primary taste qualities： sweet；
sour； bitter； and saline
5。 Taste buds may be damaged by alcohol； smoke； and acids； but the taste
system is the most resistant to damage of all sensory systems； as taste
receptors are replaced every few days； even more often than smell
receptors
C。 Touch and Skin Senses
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PSYCHOLOGY AND LIFE
1。 Cutaneous senses are sensations produced by the skin； such as pressure；
cold； and warmth。 Because the skin responds to so many types of
stimuli； many different types of receptors are located near the surface of
the skin。
2。 Meissner corpuscles respond best when something rubs against the skin
3。 Merkel disks are most active when a small object exerts steady pressure
on the skin
4。 The skin has separate receptors for hot and cold
5。 Erogenous zones are areas of the skin that give rise to erotic； sexual
sensations
D。 The Vestibular and Kinesthetic Senses
1。 Vestibular sense tells how the body is oriented in the world with respect to
gravity through tiny hairs in fluid…filled sacs and canals in the inner ear
a） The saccule and utricle detect acceleration and deceleration
b） The semicircular canals are at right angles to each other and can
thus detect movement in any direction
c） Motion sickness occurs when information from the visual system
conflicts with information from the vestibular system
2。 The kinesthetic sense provides constant sensory feedback about what the
body is doing during motor activities。 There are two sources of
kinesthetic information： receptors in the joints and receptors in muscles
and tendons
a） Receptors in the joints respond to pressures that acpany
different positions of the limbs and to pressure changes that
acpany movements
b） Receptors in the muscles and tendons respond to changes in
tension that acpany muscle shortening and lengthening
E。 Pain
1。 Pain is the body’s response to noxious stimuli that are intense enough to
cause damage or threaten to do so。 Pain is critical to survival。 People
with insensitivity to pain often bee scarred and their limbs deformed
from injuries that could have been prevented had they been sensitive to
pain。
2。 Pain mechanisms
a） Nociceptive pain is the negative feeling induced by a noxious
external stimulus； such as a hot stove
b） Neuropathic pain is caused by the abnormal functioning or over
activity of nerves
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CHAPTER 4： SENSATION
c） The network of pain receptors is a fine mesh that covers the entire
body。 Some receptors respond only to temperature； while others
respond to chemical or mechanical stimuli。
d） Peripheral nerve fibers transmit signals to the central nervous
system in two ways：
i） Fast…conducting； myelinated nerves
ii） Slower； smaller； nonmyelinated nerves
e） Pain impulses start at the spinal cord； are relayed to the thalamus；
and then to the cerebral cortex
3。 The Psychology of Pain
a） Emotional responses； context factors； and subjective interpretation
can be as important as actual physical stimuli in determining how
much pain is experienced
b） Phantom limb phenomenon is the experience of sensation or pain
in a limb that is no longer there。 It occurs in up to 10 percent of
amputees。
c） Pain is partly a psychological response and； thus； can be
influenced by psychological processes； such as hypnosis； deep
relaxation； and thought distraction。 The Lamaze preparation for
childbirth is an excellent example of the psychological control of
pain。
d） The Gate…Control Theory of pain； proposed by Ronald Melzack；
suggests that cells in the spinal cord act as neurological gates；
interrupting and blocking some pain signals and letting others
through to the brain。 The brain and receptors in the skin send
messages to the spinal cord to open or close the gates。
e） In recent years Melzack proposed an updated neuromatrix theory
of pain which incorporates the reality that people often experience
pain with little or no physical cause。
DISCUSSION QUESTIONS
1。 What other senses might there be that humans lack？ How would we know that they
existed？ How might humans develop devices； such as binoculars； night…vision scopes； and
hearing aids； which allow us to experience these senses？
2。 How similar are sensory experiences between people？ Do all individuals experience the
color “blue” the same？ How would we know if we did not； and would it matter？
3。 Have the class think of real…life examples of dichotic listening。 Is this a phenomenon with
which they are familiar and of which they have a basic understanding？
4。 Discuss attention from the perspectives of its being goal…directed or stimulus…driven
perception。 Generally speaking； do more students seem to be goal…directed attendees or
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PSYCHOLOGY AND LIFE
stimulus…driven perceivers？ What might contribute to this phenomenon？
5。 Discuss the premises of Gestalt psychology with the class。 Point out that Kurt Lewin’s
Field Theory was a result of the Gestalt movement。 What other theoretical constructions
might have a relationship to the Gestalt