The effects of masking on vibrotactile temporal summation in the detection of sinusoidal and noise signals.

Thresholds for the detection of vibrotactile signals of varied duration applied to the thenar eminence were measured in the absence of and in the presence of a masking stimulus. Signals were 250- and 500-Hz sinusoids and noise bursts with bandwidth limited to 250-1000 Hz. The masking stimulus was either a 250-Hz sinusoid, which was presented in phase with the signal when it was sinusoidal, or noise. Changes in threshold as a function of changes in signal duration were found which were predicted accurately from Zwislocki's theory [J. Acoust. Soc. Am. 32, 1046-1060 (1960)] of temporal summation when the signal was detected by the Pacinian channel, but not when it was detected by a non-Pacinian channel (NP). However, when either the signal or the masking stimulus or both were noise, NP thresholds were affected by changes in signal duration. Only when the signal and masking stimuli were both sinusoids were NP thresholds independent of signal duration. It is concluded that signal duration effects in the NP channel are not due to temporal integration, but rather to increases in information about the signal content provided to the subject as exposure duration is increased.