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The effect of altitude on tests of reaction time and alertness.

Psychomotor performance was assessed in 20 subjects on each of 2 mountaineering expeditions. During the first, which reached 5,008 m, simple reaction time and alertness were measured, on the second to 4,790 m these were replaced by a three-choice reaction time test. In both, mean reaction times increased significantly at altitude in subjects with marked symptoms of Acute Mountain Sickness (AMS), whereas the alertness tests showed no effects. Reaction times were not affected by other environmental factors but adverse conditions increased the number of errors. The increase in reaction time may be ascribed either to the lethargy associated with AMS or alternatively may have been a direct effect of hypoxia. The latter explanation is favoured because of reports by other workers of an increase in reaction time with altitude in the absence of AMS.