Human Performance under Vibrational Stress

Abstract

Blindfolded subjects, restrained by standard harness, sat on a modified Air Force chair, which was programmed to move in random patterns in pitch and roll, the subjects counteracting these motions by using a control stick. The whole device was itself mounted on a mechanical shake table producing vertical sinusoidal motion at frequencies ranging from 2 c/s to 20 c/s and at amplitudes corresponding to about one-third of the subjective tolerance limits. The angular deviations from the upright position were evaluated relative to the disturbing input for both pitch and roll, one minute during the vibration experience and one minute after cessation of the vibration. Some individual subjects were not influenced by the vibration; others showed performance decrements. In the mean, these measures of human performance reflect all mechanical resonances within the body, previously established by other methods. The frequencies most affecting performance were found to be between 3 and 12 c/s. Residual effects were detected by the measurements after vibration.