NEURAL MECHANISMS OF SCANNED AND STATIONARY TOUCH

The neural mechanisms subserving the sense of touch set the limits for the acquisition of information regarding the spatial and temporal characteristics of stimuli impinging on the skin surface. The results of three different psychophysical experiments imply that the skin of the finger pad can resolve the elements of a stimulus separated by 0. 9 mm when the stimulus is applied to the skin and held stationary. This resolution limit is only slightly improved (to about 0. 7 mm) when movement between the stimulus and skin is allowed. Single-unit recordings from the three classes of primary mechanoreceptive afferents in anesthetized monkeys shows that only one class, the slowly adapting afferents, resolve spatial detail of stationary stimuli near the resolution limit. In addition, slow adaptors appear to resolve moving stimuli (e. g. , Braille-dot patterns) more effectively than do the other two classes.