Sensation & Perception
Ch. 14: The Cutaneous Senses
© Takashi Yamauchi (Dept. of Psychology, Texas A&M
University)
Main topics
Mechanoreceptors
Temporal, spatial, & frequency responses
Cortical map
Tactile acuity
Perceiving texture
Pain perception
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The Cutaneous sensations
• Sensations based on the stimulation of receptors in
the skin.
– Pressure, vibration, heating, cooling, and tissue damage.
• It is served by the somatosensory system.
• It also creates
– Proprioception (the body sense – e.g., balancing the
body)
– Kinesthesis (the sense of the position and movement)
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• Ian Waterman (a 17 year old
butcher)
– Contracted flu.
– Damaged somatosensory
cortex
– Couldn’t
– As a result, he lost the ability to
• feel skin sensation below his
neck.
• feel his body,
• adjust his body position
• grasp objects properly.
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Skin
• “monumental façade of the human body”
– (Cornel, 1953)
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2 Layers
Skin
Epidermis
dermis
Functions of Skin:
Keeps the body warm
Protects the body from
bacteria
Help maintains the
integrity inside the
body.
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Mechanoreceptors: pick up the
movement of skin
Merkel receptor
Meissner corpuscle
Ruffin cylinder
Pacinian
corpuscle
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Mechanoreceptors
• Mechanoreceptors respond to
– mechanical stimulation such as pressure, stretching, and
vibration.
• Transduction (Pacinian corpuscle)
– When the corpuscle is bent relative to the axon, the tip
of the nerve ending opens ion channels in the
membrane.
– The opening permits the entry of molecules with
positive charge, which depolarize the membrane
potential.
– (from N. R. Carlson “Physiology of Behavior”, 7th ed)
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Fig. 14-1, p. 331
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Fig. 14-2, p. 332
Pathways from skin to cortex
Skin  spinal cord 
thalamus  cortex
• 2 pathways
• Medial lemniscal pathway
– Proprioception & touch
perception
• Spinothalamic pathway
– Temperature and pain
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Cortical map
• Somatosensory cortex
– Corresponds to body locations
• Cortical magnification
factor
– Sensitive areas occupy large
cortical areas (e.g., fingers)
• These cortical areas are
plastic (can be changed by
experience)
–  e.g., trained pianists have
larger cortical representations
of fingers.
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Perceiving details (tactile acuity)
• Measuring tactile acuity
– Two-point threshold minimum separation
needed between two
points to perceive them
as two units
– Grating acuity placing a grooved
stimulus on the skin
and asking the
participant to indicate
the orientation of the
grating
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• The density of Merkel receptors and tactile acuity is
highly correlated.
– The areas that have more Merkel receptors are more
sensitive
Merkel receptors
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Perceiving vibration
• The Pacianian corpuscle is responsible.
– Sustained stimuluation  no response
– Rapid on-off stimulation  response
Merkel
receptor
Meissner
corpuscle
Ruffin
cylinder
Pacianian
corpuscle
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Perceiving texture
• Temporal cues
– The movement of a
surface generates
vibration, which gives
the perception of texture
(rough vs. fine texture)
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Perceiving objects
• Haptic perception
– Perception, in which 3D objects are explored with the
hand.
– Involves sensory, motor, and cognitive systems.
• Demonstration
–
–
–
–
–
Identifying objects
The person sitting next to you close his / her eye.
Pick up an object (e.g., an eraser)
Let him / her touch the object and identify the object.
Swap the role.
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Perceiving Objects - continued
• Psychophysical research
shows that people can
identify objects haptically in
1 to 2 sec
• people use exploratory
procedures (EPs)
– Lateral motion
– Pressure
– Enclosure
– Contour following
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The Physiology of Tactile Object Perception
- continued
• Monkey’s somatosensory cortex also shows
neurons that respond best to:
– Grasping specific objects
– Paying attention to the task
• Neurons may respond to stimulation of
the receptors, but attending to the task
increases the response
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Figure 14.19 Receptive fields of neurons in the monkey’s somatosensory cortex. (a) This neuron responds
best when a horizontally oriented edge is presented to the monkey’s hand. (b) This neuron responds best
when a stimulus moves across the fingertip from right to left. (From “Movement-Sensitive and Direction and
Orientation Selective Cutaneous Receptive Fields in the Hand Area of the Postcentral Gyrus in Monkeys,”
by L. Hyvarinen and A. Poranen, 1978, Journal of Physiology, 283,523-537, figure 3. Copyright © 1978 by
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The Physiological Society, UK. Reprinted by permission.)
Figure 14.20 The response of a neuron in a monkey’s parietal cortex that fires when the
monkey grasps a ruler but that does not fire when the monkey grasps a cylinder. (From
“Cortical Processing of Tactile Information in the First Somatosensory and Parietal
ch 14and Y. Iwamura, 1978. In G. Gordon (Ed.),
20
Association Areas in the Monkey,” by H. Sakata
Active Touch, p. 61. Copyright © 1978 by Pergamon Press, Ltd. Reprinted by permission.)
Pain perception
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Pain Perception
• Pain comes from
– a sensory component and an emotional
component.
• Three types of pain:
– Nociceptive - signals impending damage
to the skin
• Types of nociceptors respond to heat,
chemicals, severe pressure, and cold
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Types of Pain
– Inflammatory pain
• caused by damage to tissues and joints that
releases chemicals that activate nociceptors
– Neuropathic pain
• caused by damage to the central nervous
system, such as:
– Brain damage caused by stroke
– Repetitive movements which cause
conditions like carpal tunnel syndrome
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Nociceptive (skin-oriented)
Inflammatory (tissue &
joints-oriented)
Neuropathic (nervoussystem-oriented)
ch 14 ways. See text for details. (Adapted from Scholz
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Figure 14.22 Pain can be created in a number of different
& Woolf, 2002.)
Brain areas for pain perception
– Subcortical areas
• hypothalamus,
limbic system,
and the thalamus
– Cortical areas
• S1 and S2 in the
somatosensory
cortex, the insula,
and the anterior
cingulate cortex
–  the pain matrix
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Figure 14.23 The perception of pain is accompanied by activation of a number of different areas
of the brain, including the somatosensory cortex,
thalamus, anterior cingulate cortex, amygdala,
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hippocampus, and thalamus. The ring-like configuration formed by the anterior cingulate cortex,
hippocampus and amygdala form the limbic system.
What does this tell?
• Cognitive control can modify pain
– Interpreting stimuli (suggestion, recognition)
– Shifting attention (think about something else)
– Expectation (e.g., placebo effect  fake
medicine can be sometimes effective)
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Cognitive and Experiential Aspects of Pain
• Expectation - when surgical patients are told
what to expect, they request less pain
medication and leave the hospital earlier
• Shifting attention - virtual reality technology
has been used to keep patients’ attention on
other stimuli than the pain-inducing
stimulation
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Cognitive and Experiential Aspects of Pain continued
• Content of emotional distraction - participants
could keep their hands in cold water longer
when pictures they were shown were positive
• Individual differences - some people report
higher levels of pain than others in response
to the same stimulus
– This could be due to experience or to
physiological differences
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Figure 14.25:
Participants kept
their hands in cold
water longer when
looking at positive
pictures than when
looking at neutral or
negative pictures.
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