Mechanisms of vibration-induced interference with manual control performance

An experiment is described in which eight subjects performed three simple tasks (A, B and C) in static conditions and during exposure to whole-body vertical (z-axis) vibration at 0.5 and 4.0 Hz, at an acceleration magnitude of 2.1 ms-2 r.m.s. All subjects performed all conditions with and without an arm support. The objective was to explore the mechanisms that may cause disruption of manual control performance during vibration exposure. With task A subjects simply held a control with no visual feedback of activity at the control. With task B, subjects used the control to hold a controlled element stationary on a display. Task C was the same as task B, except that subjects had improved visual feedback of movement of the controlled element. Results showed that both 0.5 and 4.0 Hz vibration caused significant increases in control activity at frequencies of up to about 1 Hz compared with the condition without vibration. With visual feedback in task C, subjects were able to detect drifting of the controlled element on the display and introduced compensatory control activity at frequencies above about 0.2 Hz. The arm support reduced the magnitude of vibration transmitted to the control at 4.0 Hz, but did not otherwise change the results.