THE EFFECT OF STIMULUS-DURATION ON FREQUENCY-RESPONSE FUNCTIONS IN THE PACINIAN (P) CHANNEL

Psychophysical experiments on human observers and physiological measur ements on Pacinian corpuscles (PCs) isolated from cat mesentery were p erformed to explain certain discrepancies in the psychophysical-physio logical model (Bolanowski et al., 1988) for the sense of touch in the vibrotactle Pacinian (P) channel. The model was based on correlations among the psychophysical frequency response obtained on human glabrous skin and physiological frequency-response functions measured on two P C preparations: PC fibers innervating human glabrous skin (Johansson e t al., 1982) and PCs isolated from cat mesentery. The three frequency- response functions were qualitatively similar. However, the low-freque ncy slope for the human PC fibers differed from the slopes for the psy chophysical and cat mesentery PC functions by being 3 dB/octave less s teep. This discrepancy can be explained theoretically by differences i n methodology involving the effect of stimulus duration and the proper ty of temporal summation known to exist in the P channel (i.e., a 3-dB increase in sensitivity per doubling of stimulus duration). To test t his, experiments were performed using two methods of stimulation: (1) a constant stimulus duration for different test frequencies, as genera lly used in this laboratory; and (2) a constant number of stimulus cyc les (n = 5) for each test frequency as used by Johansson et al. The me thod of least squares was used to calculate the low-frequency (50 to 1 50-Hz) slopes of individual psychophysical and physiological functions . The mean slopes that resulted from using the two methods of stimulat ion were consistent with the theoretical expectations.