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 Pacinian (P) or a non-Pacinian (NP I) channel. Brief masking and test stimuli 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 ( Delta t) between the masking and test stimuli that ranged from 5 to 995 microseconds. Masking stimulus level was also varied from 5 to 25 dB above threshold. The masking effect followed an exponential decay with different time constants for each of the channels, but a similar asymptote (residual masking) for both channels. At the higher masking stimulus levels, the time constant for the P channel was about 40 microseconds, while the time constant for the NP I channel was about 100 microseconds. Residual masking in both channels increased about 1 dB for every 5-dB increase of masking stimulus level.