Abstract

Temporary threshold shifts (TTSs) in vibrotactile perception produced by continuous vibration and repetitive shock have been investigated. Subjects were exposed to vertical hand-transmitted 100 Hz continuous vibration and various repetitive shocks of equal energy content formed from one complete cycle of a 100 Hz sine wave. The repetition rate of the cycles was 5, 25, 50, or 100 s-1 while the root-mean-square (rms) acceleration measured over exposures of five minutes was held constant at 2.5, 5, or 10 ms-2 rms (weighted according to British Standard (BS) 6842 and International Standard (ISO) 5349). A control condition with no vibration was also included. Subjects held a handle with 10% of their maximum hand grip force. When exposed to five shocks per second at each of the three frequency-weighted acceleration magnitudes the subjects developed a small TTS. Exposure to 100 shocks per second (continuous vibration) at each of the three frequency-weighted acceleration magnitudes caused a large TTS, although the total frequency-weighted energy was the same as when exposed to five shocks per second. The relation between the TTS, the logarithm of the shock repetition rate, and the logarithm of the frequency-weighted rms acceleration was described by the relation TTS = -16.256 + 11.812 log10 R + 15.179 log10 ahw, where TTS is the temporary threshold shift, R is the shock repetition rate, and ahw is the frequency-weighted rms acceleration according to BS 6842 and ISO 5349. The results suggest that the equal energy hypothesis underlying BS 6842 and ISO 5349 is inappropriate for the prediction of the TTS produced by repetitive shocks.