Cutaneous stimuli, vibratory and saltatory.

Cutaneous vibratory stimuli typically involve only a single point of contact with the skin, even though there is likely to be widespread propagation of the disturbance through it. If two or more somewhat widely separated contactors are made to share the individual impacts, seriatim, some new phenomena arise. A systematic mislocalization results if the temporal relations between two successive pulses fall within the limits of 20 to 260msec. The apparent displacement of cutaneous taps is regular and predictable; it is determined mainly by time but secondarily by pulse intensity. Control experiments show that the leaps from the veridical position ("saltation") are not to be accounted for by traveling waves in the skin; direct electrical stimulation elicits the same phenomena. Moreover, the same saltatory jumps can be evoked with hot and cold stimuli serving as attractants, with the time relations remaining unchanged. The saltatory leaps are also found even when the intervening skin is anesthetized. Compelling evidence shows the saltation effect to have a central seat. The fact that saltatory leaps apparently do not transcend dermatomal boundaries is of considerable neurologic importance. Attempts to identify the underlying mechanism of saltation have led to further evidence of the metastability of sensory systems.