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not pure tones； which is reflected in timbre。
D。 The Physiology of Hearing
1。 In order for hearing to occur； four basic energy transformations must
take place
a） First； airborne sound waves must be translated into fluid waves
within the cochlea of the ear。 Sound waves travel into the ear until
they reach the end of the canal。 There they encounter the tympanic
membrane or eardrum。 The sound waves move the eardrum； and
the eardrum transmits the vibrations from the outer ear to the
middle ear； which contains the hammer； the anvil； and the stirrup。
These tiny bones transmit the vibrations from the eardrum to the
primary organ of hearing； the cochlea in the inner ear。
b） Second； the fluid waves must stimulate mechanical vibrations of
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PSYCHOLOGY AND LIFE
the basilar membrane。 Vibration of fluid in the cochlea causes a
coiled tube membrane in the cochlea； the basilar membrane； to
move in a wavelike fashion。
c） Third； these vibrations must be converted into electrical impulses。
The wavelike motion of the basilar membrane bends tiny hair cells
connected to the membrane。 As the hair cells bend； they stimulate
nerve endings； transforming the wave motion into neural activity。
d） Fourth； the impulses must travel to the auditory cortex from the
cochlea via the auditory nerve。 Information from one ear goes to
both sides of the brain。
2。 There are two types of hearing impairment； each caused by a defect in
one or more ponents of the auditory system： conduction deafness
and nerve deafness
a） Conduction deafness is the less serious of the two and involves a…
problem in the conduction of air vibrations to the cochlea。 It can
often be corrected by the insertion of artificial anvils or stirrups。
b） Nerve deafness is more serious and involves a defect in the neural
mechanisms that create nerve impulses or that relay them to the
auditory cortex
E。 Theories of Pitch Perception
1。 Two major theories have been posited to explain sensations of pitch：
place theory and frequency theory
a） Place theory； proposed first by Helmholtz and later modified by
Bekesy； suggests that different portions of the basilar membrane
move depending on the frequency of the sound wave。 High…
frequency tones produce greatest motion at the base of the cochlea；
while low…frequency tones produce the greatest motion at the
opposite end。
b） Frequency theory suggests that the rate of vibration of the tone is
reflected in the rate of vibration of the basilar membrane。 If a tone
vibrates at 100 Hz； the basilar membrane will also vibrate at 100
Hz and will cause neurons to fire at 100 Hz。 For high…pitched
sounds； however； this is impossible； because they cannot fire more
than 1；000 times per second。 The volley principle may overe
this limitation。
2。 The Volley Principle suggests that several neurons could work together
and could fire in a volley to match higher cycles per second
3。 Frequency and Place Theories are not mutually exclusive。 Place theory
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 ex