Effects of whole-body vibration waveform and display collimation on the performance of a complex manual control task

An experiment is described in which two independent groups of eight subjects each performed a combined continuous and discrete tracking task during exposure to vertical whole-body vibration. Both groups received sinusoidal and random vibration at preferred third-octave centre frequencies of 0.5-10 Hz. One group performed the task with the display collimated by a convex lens. Without the collimation, performance was disrupted by both types of vibration at all vibration frequencies; collimation removed the disruption at frequencies above 1.6 Hz. There were differences in the effects of random and sinusoidal vibration at 2.0 and 2.5 Hz, suggesting that compensatory eye movements were assisting performance during exposure to the predictable sinusoidal motion. The results show that continuous control performance was disrupted by visual interference at frequencies above 1.6 Hz; closed-loop system transfer functions showed that visual interference increased the phase lags which impaired control performance. Possible mechanisms explaining the disruption in performance at lower frequencies are discussed.