Mechanisms of the effects of vibration frequency,level and duration on continuous manual control performance

This paper describes three experiments, performed to determine the effects of vibration frequency, level and duration on a zero order, pursuit tracking task, and to discover the mechanisms responsible for these effects. The first experiment investigated the effect on tracking performance of vertical, sinusoidal vibration of the control stick in the frequency range 4 to 64 Hz. Control dynamics were either isotonic (displacement), isometric (force) or spring-centred. The second experiment investigated the effect of level of vertical, 4 Hz and 16 Hz whole-body and control vibration on performance with the isotonic and isometric controls. Experiment 3 investigated the effects of duration of continuous, vertical, whole-body vibration at 4 Hz, for durations up to 1 h, on performance with the isotonic and isometric controls. Performance measures included closed-loop transfer functions of the human operator and components of mean-square tracking error correlated with the forcing functions and vibration, and those due to operator-generated noise or remnant.

The results indicated that the primary effects of vibration on the tracking task were increases in remnant and vibration-correlated error. Perceptual and motor sources are suggested for the increased remnant. The effects were largest with 4 Hz vibration and were found to be effectively constant throughout 1 h exposures to continuous 4 Hz whole-body vibration, but after relatively short periods the effect on overall tracking performance was effectively masked by large increases in response lags and suppression of coherent responses, which occurred in both static and vibration conditions as a consequence of diminished levels of arousal.