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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

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The Skin

Receptors in the Skin

From the Skin to the Brain


Touch

Afferent Systems for Touch

Passive Touch

Demonstration 12.1 Two Point Discrimination Thresholds

Find 2 toothpicks and hold them together so that the points can both touch your skin at the same time.  Separate the toothpicks by about 1 cm.  Touch your cheeks with the toothpicks and describe the sensation.  Now touch your calf with the toothpicks and notice whether the sensations are different.  Move the toothpicks closer together and touch your cheek again.  How close together can the toothpicks be before you perceive a single touch?  Now move the toothpicks farther apart and touch your calf again.  Continue to move the toothpicks apart until you can feel two distinct touches on your calf.  How far apart can they be moved until you feel the two distinct touches?

Demonstration 12.2 Touch Adaptation

Place a square piece of paper the size of a pea on the hairy-skin side of your hand and notice how long it takes until you can no longer feel the paper.  Repeat this exercise with the glabrous-skin side of your hand.  Continue these comparisons in touch adaptation by trying stimuli of different sizes and weights and on different regions of both sides of your hand.  Compare touch adaptation in both locations and notice the general phenomenon of touch adaptation.

Touch Adaptation Touch Adaptation 2
Photo by R. Oldmixon

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.

Ten Items
Photo by R. Oldmixon

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.

Link - International Society for Haptics.

Interactions between Touch and Vision

 


Temperature

Afferent Systems for Temperature

Thresholds for Temperature

Demonstration 12.4 Temperature Sensitivity

Find a metal fork or spoon.  Touch the bottom of the handle to your forehead, chest, stomach, shoulder, arm, foot, and calf.  Notice that the handle feels cold when you touch some parts of your body, but its temperature is not noticeable on other body parts.  Now run hot water on the utensil handle, wipe it off quickly, and touch it to your forehead.  Repeat this process for each body part where you tested the spoon originally.  Where is the heat most noticeable?  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 have been testing.  Where is the cold most noticeable?

Spoon to Forehead
Photo by R. Oldmixon

Adaptating to Temperature

Demonstration 12.5 Temperature Adaptation Find 3 bowls. Fill one with very hot tap water (but not so hot that it is painful), another with very cold tap water, and a third with a mixture of water from the other two bowls (this will give you lukewarm water). Arrange the three bowls so that the cold water is on your right, the hot water is on your left, and the lukewarm water is in the middle. Place your right hand in the cold water and your left hand in the hot water. Leave your hands in these bowls for approximately 3 minutes and then quickly transfer both hands to the lukewarm (middle) bowl.  Notice the apparent temperature of each hand.


Pain

• 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.

Phantom Limbs and Pain

Measuring Pain

Adapting to Pain

Controlling Pain

 


Kinesthetic and Vestibular Senses

Kinesthetic Sense

Demonstration 12.6 The Pinocchio Effect This one may be a little weird.  You’ll need a good friend and two chairs.  First, set up the two chairs, one behind the other.  Now, sit in the first chair, and have your friend sit in the chair right in front of you. Close your eyes and have your friend take your dominant hand and place it on their nose. Here comes the weird part.  Put your other hand on your own nose.  Start tapping and stroking your friend’s nose at random intervals, the more random your movements, the better this works.  Imitate these movements on your own nose.  Try to make the movements synchronize as best as possible.  Continue this for thirty seconds to a minute.  If you are susceptible, you may start to feel as if your nose is three feet long!  Not everyone will feel it, so don’t worry if you try it a few times and you don’t feel anything different.

Nose Goes
Photo by R. Oldmixon

Demonstration 12.7 The Importance of Kinesthesia Close your eyes and extend your arms out at your sides. Point your index fingers. Now bring your index fingers quickly towards each other in front of your body.  Can you touch your two fingers with your eyes closed? Try this task several times and assess your success. Then close your eyes and use an index finger to touch each of your toes. Repeat this exercise several times to assess your success. You might also be interested in testing whether you are equally successful at touching your index fingers together behind your back; most people are somewhat less accurate at this task.

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.

Vestibular Senses
Photo by R. Oldmixon

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.


Test Yourself

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?

 


Teaching Materials

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.


Recommended Readings

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.