The effects of a surround on vibrotactile thresholds: evidence for spatial and temporal independence in the non-Pacinian I (NPI) channel.

Detection thresholds were measured for sinusoidal vibrations applied to the thenar eminence and volar forearm. Stimuli were applied via a 0.72-cm2 circular contactor, with and without a rigid surround. At low frequencies, below about 40 Hz, the thresholds were higher without the surround than with the surround. However, in contrast to earlier reports, the shape of the threshold function was the same with and without the surround, suggesting that the temporal and spatial tuning characteristics of the non-Pacinian I (NPI) channel are independent.