SENSORY AND PHYSIOLOGICAL BASES OF TOUCH
Roger W. Cholewiak Amy A. Collins Princeton University
Touch has been defined as the variety of sensations evoked by stimulation of the skin by mechanical, thermal, chemical, or electrical events. Even Aristotle, in dividing our contact with the world into the five senses, was doubtful that "touch" described but a single sense. Because there is such a variety of sensations aroused by stimuli interacting with the skin, it might be more appropriate to describe this modality as the "senses of touch." And, as befits such a symphony of sensations, there are a multitude of instruments contributing their voices, each in its own fashion. The mechanical and physiological characteristics of the skin and these receptor structures, as with those in other senses, define and limit the sensitivity of the skin to stimuli. In most of this chapter we will be describing the anatomy and morphology of those structures, both visible and below the surface, that constrain and define the events that eventually will evoke a tactile sensation. In the remainder of the chapter, there will be a discussion of the most basic measures of the skin's sensitivity. The issues involved with the processing of more complex tactile stimuli will be presented in other chapters in this volume.
Touch, for the most part, is a proximal sense. That is, we feel those things that either are close to us or actually contact us. There are exceptions to the strict interpretations of this notion: We feel radiant heat, for example, as well as the deep bass of the opening chords of Also Sprach Zarathustra (the 2001 movie theme) or heavy metal rock music! These events produce