Inverse relationship between task complexity and performance deficit in 5 m water immersion

Previous research on cognitive deficits during shallow water immersion led to inconsistent results: some authors observed deficits at 5 m, but others only at depths well beyond 5 m. The present study evaluates whether this discrepancy could be related to different levels of difficulty. Forty-eight subjects participated in a mental rotation task and in a color-word task, both having multiple levels of difficulty. The two tasks were administered once 5 m below the water's surface and once on dry land. Compared to land, subjects' reaction time increased in 5 m depth when task difficulty was low, but it did not increase when task difficulty was high. Thus, performance deficits in 5 m depth were inversely related to task complexity. We interpret this counter-intuitive finding within the framework of a multiple-channel parallel processing model, with channels that are differentially sensitive to immersion. This model correctly predicts performance deficits on simple, but not on complex skills at smaller depths, and deficits on simple as well as complex skills at larger depths, in accordance with the present findings and data from literature.