DECAY IN THE EFFECT OF VIBROTACTILE MASKING

Vibrotactile forward masking experiments were conducted on the thenar eminence of the hand to determine the time course of masking in the Pa cinian (P) or a non-Pacinian (NP I) channel. Brief masking and test st imuli that contained energy centered either below 27 or at 500 Hz were used to preferentially activate the NP I or P channels. respectively. Test thresholds were measured at different fixed delays (at) between the masking and test stimuli that ranged from 5 to 995 ms, Masking sti mulus level was also varied from 5 to 25 dB above threshold. The maski ng effect followed an exponential decay with different time constants for each of the channels, but a similar asymptote (residual masking) f or both channels. At the higher masking stimulus levels, the time cons tant for the P channel was about 40 ms, while the time constant for th e NP I channel was about 100 ms. Residual masking in both channels inc reased about 1 dB for every 5-dB increase of masking stimulus level. ( C) 1996 Acoustical Society of America.