Cognitive impairment during 5 m water immersion.

Experimental data document that human cognition remains intact down to 6 m water immersion. This, however, is difficult to reconcile with introspective observations from experienced divers, who report cognitive impairments. We hypothesized that the discrepancy might be related to the fact that previous experiments assessed abstract cognitive skills, such as mental arithmetic, which might be less sensitive to immersion than performance-related cognitive skills, such as planning of behavior that is adequate for a given situation. Moreover, previous studies did not control for the effects of water viscosity on subjects' response times. To address these issues, the present study evaluated performance-related cognitive skills based on subjects' isometric responses. Forty-eight subjects were tested in 5 m under water and on dry land using multiple choice reaction tasks, a tracking task, and a combination of both. Sustained attention was also registered, and subjective workload was assessed by questionnaire. We found that a subject's cognitive performance was degraded under water by 9%, independent of task type and equally under single- and dual-task conditions. Sustained attention was reduced under water by 11% and tracking by 48%. The observed deficits were not correlated, which suggests multiple independent effects of immersion. Our findings support the hypothesis that performance-related cognitive skills are affected already by shallow-water immersion. Since no such deficits were observed in a companion study just below the water's surface, the present findings are probably due to increased ambient pressure.