The Skin Senses
Demonstrations (Direct Links)
Demonstration 12.1 Two-point Discrimination Thresholds
Demonstration 12.2 Touch Adaptation
Demonstration 12.3 Haptic Perception of Objects
Demonstration 12.4 Temperature Sensitivity
Demonstration 12.5 Temperature Adaptation
Demonstration 12.6 The Pinocchio Effect
Demonstration 12.7 Kinesthesia
Demonstration 12.8 Vestibular Sense
Before You Start
•
•
•
Receptors in the Skin
From the Skin to the Brain
Afferent Systems for Touch
Passive Touch
Link - You can see a demonstration of the rubber hand illusion on YouTube.
Active Touch
• Demonstration 12.3 Haptic Perception of Objects
First assemble 10 miscellaneous objects of similar sizes that you find in your room. Place them on your desk and close your eyes. Identify an object by exploring it with active touch. Pay attention to how you move your fingers around an object to determine its identity. Next determine the hardness of your desktop and other nearby objects. Do you use your hands differently than you did when identifying objects? Finally, use your fingers to determine the texture of your shirt and other objects. You should again notice that your fingers move in a different fashion to perform this task.
Link - Randy Flanagan heads the Cognition & Action Laboratory (Queen's University), maintaing web pages that illustrate his research on the way we interact with the world.
Link - The Haptic Community Web Site (Northwestern University) provides a number of links, etc., that are useful to those who would like to learn more about haptic research.
Interactions between Touch and Vision
Afferent Systems for Temperature
Thresholds for Temperature
• Demonstration 12.4 Temperature Sensitivity
To test for temperature thresholds with cold stimuli, place a bunch of pennies in a freezer for a couple of hours. Touch the pennies to the same body parts you tested earlier. Where is the cold most noticeable?
Adaptating to Temperature
• The International Association for the Study of Pain defines pain as “an unpleasant sensory and emotional experience associated with actual or potential tissue damage . . .”
• Link - Oprah Winfrey hosted a show on which a child with congenital insensitivity to pain appeared. You can also watch a documentary on children with congenital insensitivity to pain.
Afferent and Efferent Systems for Pain: Gate Control Theory
• Link - The John C. Liebeskind History of Pain Collection at UCLA's Louise M. Darling Bioledical Library.
Measuring Pain
Adapting to Pain
Controlling Pain
Kinesthetic and Vestibular Senses
Kinesthetic Sense
Vestibular Sense
• Demonstration 12.8 Importance of the Vestibular Sense
Stand up and lift one leg. Notice how your body automatically adjusts to retain your balance in this somewhat precarious position. Now repeat this exercise with your eyes closed. You should find the task to be much more difficult. Vision clearly aids the vestibular sense in maintaining body balance. As one final illustration, first spin around rapidly and then try to stand on one leg. The unusual stimulation of your vestibular sense caused by spinning around will make the task very difficult—even with your eyes open. Thus, the vestibular sense must be very important for maintaining our balance.
• Link - NASA has several pages discussing the impact of space flight on the vestibular system.
• Link - Kathleen Cullen (McGill University) heads the Vestibular Neurophysiology and Gaze Control Laboratory.
1. Refer to material in the chapter to explain each of the following observations
about touch:
a. Something touches your leg, and you have
no idea what shape it is; then it touches your face, and its shape seems clear.
b. The fabric on a chair seems rough against
your arm when you first sit down, but you do not notice it after 5 minutes.
c. You’ve placed your sleeping bag on
a surface without noticing that a twig is underneath. In reality, the twig
has two prominent points, yet when some parts of your body rest on the twig,
it seems like a single point.
2. Heller’s research suggests several advantages in touch perception
for people who are not blind from birth. If you are now sighted, imagine
that you found out that you were going blind. Describe specific things you
could do to take advantage of the advance notice that you’re going
blind. Once you were completely blind, how would your perceptual experience
differ from that of sighted people?
3. In this chapter we discussed thresholds for touch, temperature (both warmth
and cold), and pain. We saw that each of these thresholds varied from one
part of the body to another. Summarize the findings on these various kinds
of thresholds and note the similarities and differences.
4. Adaptation has been a recurring theme throughout the text. Discuss adaptation
to touch, temperature, and pain. Think of an example of each of these kinds
of adaptation from your own recent experience. Can you think of an occasion
when adaptation did not occur? Try to relate the experience of adaptation
in these senses to adaptation in other senses.
5. What is pain, why does it differ from other perceptual experiences, and
why are its thresholds different? What function does pain serve? What is
phantom limb pain and what does it tell us about theories of pain perception
in particular and perception in general?
6. Discuss specificity theory and pattern theory, both in their application
to the general skin senses and in their application to pain perception. Would
the discovery of specific transient receptor potential (TRP) or sodium channel
proteins support specificity theory? Describe the gate-control theory, considering
the extent to which it supports a specificity or pattern approach to understanding
pain.
7. Throughout the text, we’ve emphasized the importance of central
processes in perception. Explain why each of the following topics documents
the importance of central psychological processes in pain perception: (a)
phantom limb pain, (b) placebo effect, (c) acupuncture, (d) cognitive-behavioral
approaches, and (e) hypnosis. Then discuss other aspects of touch perception
that indicate the operation of central processes.
8. Where are your hands right now? How do you know? Given research on the
rubber hand illusion, people are easily confused about the location of their
limbs. Why are we not constantly confused about the location of our limbs?
How might you link research on kinesthesia to Melzack’s notion of the
neuromatrix?
9. People such as McCredie, Angelaki, and Cullen argue that our sense of
balance should be considered a sixth sense. Explain the multisensory information
that enables us to maintain a sense of balance. How might you argue that
balance should be considered a separate sense?
10. Compare the senses discussed in this chapter with vision and hearing.
Mention, for example, (a) the nature of the stimuli, (b) the size of the
sensory systems, (c) the kind of receptors, and (d) the sensitivity of the
systems. How do the senses work together to provide a “picture” of
the world? What happens when the senses provide conflicting information?
Lafayette Instrument Co. provides several useful instruments for testing skin sensitivity, including two- and three-point aesthesiometers, pinwheel aesthesiometers, a Tactile Form Recognition Test, and a whole caseload of touch devices (Quality Cutaneous Sensitivity Kit). They also have a set of weights to test weight discrimination abilities.
Denoyer-Geppert produces a whole range of three-dimensional models, including models of the skin and spinal cord.
Link - Michael Mann (University of Nebraska) has placed his physiology textbook online, and it includes two chapters (Chapter 5 and Chapter 6) that discuss the skin senses.
Link - Haptics-e, an electronic journal for haptics research.
Link - TouchGraphics makes the Talking Tactile Tablet and other assistive devices.
Link - The Tiresias site has links to a number of different companies that produce assistive devices.
Angelaki, D. E. & Cullen, K. E. (2008). Vestibular system: The many facets of a multimodal sense. Annual Review of Neuroscience, 31, 125-150.
Benzon, H. T., Rathmell, J. P., Wu, C. L., Turk, D. C., & Argoff, C. E. (Eds.) (2008) . Raj’s practical management of pain (4th ed.) Philadelphia: Mosby.
Lackner, J. R. & DiZio, P. (2005). Vestibular, proprioceptive, and haptic contributions to space orientation. Annual Review of Psychology, 56, 115-147.
McCredie, S. (2007). Balance: In search of the lost sense. New York: Little, Brown.
Rieser, J. J., Ashmead, D. H., Ebner, F. F. & Corn, A. L. (Eds.) (2008). Blindness and brain plasticity in navigation and object perception. New York: Erlbaum.
Wall, P. D. & Melzack, R. (Eds.) (2005). Textbook of pain (5th Ed.) Churchill-Livingstone.
