Relationship between pulse rate and pulse width for a constant-intensity level of electrocutaneous stimulation

The relationship between pulse rate (PR) and pulse width (PW) for a constant level of electrocutaneous stimulation was ascertained using the method of comparative judgments. Twelve volunteer subjects were asked to adjust the PW of Comparison Stimulus (S2) until its intensity matched that of a Standard Stimulus (S1) for which the PW was 200 microseconds and PR was 10 or 20 pulses per sec (pps). As expected, the experimental results indicate that the PW of a constant-current amplitude pulse train should decrease as its PR increases if a constant level of tactile stimulation intensity is desired. However, PW and PR were not linear-inversely related (p less than 0.005). Rather, their relationship was best described by a logarithmic equation: log PW = a + b log PR, where PW is in microseconds, a is 2.82, b is -0.412, and PR is between 1 and 100 pps. Utilization of this relationship during electrical stimulation of the skin sense will decouple the intensity component of the tactile sensation from its frequency component, thereby enhancing the potential comfort and clarity of this sensory communication interface.