Quantification of reaction time and time perception during Space Shuttle operations.

A microprocessor-based test battery containing simple reaction time, choice reaction time, and time perception tasks was flown aboard a 1985 Space Shuttle flight. Data were obtained from four crewmembers. Individual subject means indicate a correlation between change in reaction time during the flight and the presence of space motion sickness symptoms. The time perception task results indicate that the shortest duration task time (2 s) is progressively overestimated as the mission proceeds and is statistically significant (p less than 0.01) when comparing preflight and postflight baselines. The tasks that required longer periods of time to estimate (8, 12, and 16 s) are less affected.

The effects of acceleration forces on night vision.

The effects of Gy and Gz acceleration forces on cone-type mesopic vision threshold values are examined. An experiment has been conducted on the Dynamic Environment Simulator, a three-axis human centrifuge, to reproduce an acceleration environment in a simulated night-flight combat situation. Acceleration environments studied were levels of +1 Gz, + 1Gy, +1.4 Gz, +2 Gz, +3 Gz, and +2 Gy in combination with +1 Gz. A visual task was performed which determined 20/50 visual acuity illumination threshold values. Physiological parameters recorded were arterial oxygen saturation (SaO2) by ear oximetry, heart rate, and visual acuity threshold values. There were 10 male subjects, all members of the United States Air Force. Their ages ranged from 25-39 years (mean +/- S.D., 29.1 +/- 4.3). Results were zero means obtained by self-pairing with +1 Gz controls. Analysis was done by self-pairing, two-tailed t test. Results showed no significant shift in luminance threshold values at +1 Gy or +1.4 Gz, and significant increases in luminance thresholds at the 0.01 level for +2 Gz, +3 Gz, and +2 Gy in combination with +1 Gz.

The acquisition and validation of the surface electromyogram signal for evaluating muscle fatigue.

The advent of new USAF aircraft control concepts necessitates the investigation of muscle fatigue in complex dynamic environments. The Acceleration Effects Branch of the Aerospace Medical Research Laboratory at Wright-Patterson Air Force Base had undertaken such a study for evaluation of fatigue in lateral G environments. Investigation of the literature indicates that the Fast Fourier Transform (FFT) of the electromyogram (EMG) signal samples could be used to determine fatigue by analysis of the center frequencies and amplitudes of the sampled power spectra. Reproducibility of data, especially in a dynamic environment, proved to be a challenge. However, acquisition and processing of the EMG signal have been optimized to give consistently reproducible and useable data. The method of sampling data and its processing are discussed.