Paradoxes in Tactile Adaptation. Focus on “Vibratory Adaptation in Cutaneous Mechanoreceptive Afferents” and “Time-Course of Vibratory Adaptation and Recovery in Cutaneous Mechanoreceptive Afferents”

Abstract

Whenever we manipulate an object, or explore it using touch, sensory adaptation occurs in some form and this is likely to have an impact on perception and probably on sensorimotor control. Adaptation may be occurring at the level of the skin and receptor, at a central level, or some combination of the two. Although it has been known for many years that adaptation occurs (Berglund and Berglund 1970), its cause and nature remain uncertain. In the tactile system, usage of the term adaptation has been somewhat loose and potentially confusing. One common use is in the classification of neural responses. For example, rapidly adapting afferents (FAI or RA, and FAII or PC) respond only to the dynamic components of a stimulus applied to the skin, whereas slowly adapting afferents (SAI and SAII) respond to both the dynamic and static components of the stimulus (Talbot et al. 1968). This type of adaptation, or filtering, has a time course of the order of a second or less and is most likely attributable to the mechanics of the receptor (Loewenstein and Skalak 1966). The second—and markedly different—way in which adaptation has been used is most evident in the large number of psychophysical studies that show that a prolonged vibratory stimulus results in a decrease in the subject’s sensitivity to a subsequent vibratory stimulus (Berglund and Ber