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KEY WORDS: touch, tactile patterns, thermal sensitivity, haptics, pain
ABSTRACT
In this review we focus on the perceptual and psychophysical aspects of somesthesis, although some information on neurophysiological aspects will be included as well; we look primarily at studies that have appeared since 1988. In the section on touch, we cover peripheral sensory mechanisms and several topics related to spatial and temporal pattern perception, specifically measures of spatial sensitivity, texture perception with particular emphasis on perceived roughness, complex spatial-temporal patterns, and the use of touch as a possible channel of communication. Other topics under this section include the effects of attention on processing tactile stimuli, cortical mechanisms, and the effects of aging on sensitivity. We also deal with thermal sensitivity and some aspects of haptics and kinesthesis. In the section on pain, we review work on the gate-control theory, sensory fibers, and higher neural organization. In addition, studies on central neurochemical effects and psychophysics of pain are examined.
INTRODUCTION
Workers in somesthesis have often complained of the difficulty of conveying to others the importance of the sense of touch and position. For vision and audition, one can imagine being deprived of sight or hearing, and there are, of course, blind and profoundly deaf individuals who can help us understand the nature of their experiences. A head cold lets us know the information derived from olfaction, but what would it be like to be without somesthesis? In May 1971, Ian Waterman lost all sensation of light touch and kinesthesis below his neck. The probable cause was a viral infection that destroyed the functioning of the large-diameter, peripheral fibers. The book Pride and a Daily Marathon (Cole 1995), a popular scientific account of Mr. Waterman's experiences, provides a description of what it is like to lose the sense of touch and position. Mr. Waterman must monitor all movements visually. If the lights go out unexpectedly, he falls down. He still has temperature sensitivity and experiences pain (cf large-diameter) consistent with neurophysiological evidence of the involvement of small diameter fibers in these modalities. The book allows readers to appreciate the importance of somesthesis and the extraordinary lengths to which a person must go to cope with its loss. With regard to the personal experience of...