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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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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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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 movement？
6。 Discuss the wide variance that exists among people in their sensitivity to pain。 The
sensation of pain is a plex process involving multiple nerve pathways。 But to some
degree； responses to pain might be learned。 In the 19th century； writers often noted that
Native Americans were remarkably stoic in the face of what Whites considered
overwhelming pain。 Other researchers have also noted cultural differences in pain
threshold。 While individual differences can easily be chalked up to differences in biological
makeup； cultural differences are more difficult to pass off as exclusively biological in
origin。
7。 Could it be that to some degree we learn how to respond to pain messages based on factors
such as how much attention we receive for crying in response to pain when we are infants？
Many parents of young children have remarked about incidents where their child has
fallen； and then looked up at the parents as if asking “How should I react？” If the parents
start to make a big fuss over the fall； the child immediately starts to cry。 If the parents smile
and stay calm； the child ignores the fall and returns to playing。 If a parent constantly
overreacts to small falls； and lavishes attention on a child every time he or she cries； could
they be reinforcing a tendency to react negatively to any pain and use overblown reactions
to pain as a means of getting attention？ Could this influence those children to be more
sensitive to any painful stimuli in that they learn to attend more to pain messages and
subsequently notice them more？ Ask students these questions to see what they think。
8。 Many people believe the myth that when people lose one of their physical senses； their
other senses bee more sensitive to pensate for the missing sense。 The idea that
blind people have hearing that is more acute than others has been around for ages。 Ask
students if they have heard this and if they believe it。 This myth is technically wrong in that
there is no actual increase in physical ability to detect sound when someone goes blind。 But
blind people may learn to pay more attention to subtle differences in sound than do sighted
people； therefore making it seem as if their hearing has increased in its sensitivity。
Similarly； losing one’s hearing does not increase one’s visual acuity； but deaf people often
pay more attention to certain visual cues than do those who can hear； allowing them to
learn more from those cues。
9。 Usually these myths focus around hearing and sight。 If the myths were true； what sense
might bee more acute if the sense of taste is lost？ Smell？ Taste？
10。 What sense would bee more acute if the sense of touch was lost？ Again； people can
sometimes pensate for the loss of a sense in a variety of ways； but there is no
pensatory increase in physical ability in the remaining senses。
SUPPLEMENTAL LECTURE MATERIAL
Sensation and Perception
Why do we study sensation and perception？ Primarily because it is through the sensory systems
that we make and maintain our contact with the environment。 What are some of the reasons that
figure into this contact with the environment？ There are many reasons； but some of the more
pertinent follow。
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1。 For purposes of munication to and from the brain； between our internal and external
environments。
2。 For organizational and functional principles that are applicable across the various sensory
and perceptual systems。
3。 For prehension of anatomical structure at a physiological level。
4。 For assistance with deficits in the various systems； such as abnormalities； deficiencies；
prosthetics； and so on。 This is especially important in vision and audition； in that
“normal” individuals get 80 percent of their sensory input through vision and 15—18
percent through audition。 The remaining 2—5 percent is distributed across the other
various systems。
5。 Finally； for philosophical reasons； to what extent is our world experience predicated on
sensation and perception？ On what else could it be predicated？
Other principles and properties that are characteristic of all sensory systems include the following：
1。 Limit