STEREOSCOPIC ACUITY UNDERWATER

Abstract
The ability of individuals to tell which of several objects is closer or farther away was tested in water of varying clarity and compared with the same performance in air. It was found that, even when the water was very clear, performance was worse than it was in air, and it became poorer as the water got more turbid. When the subjects were working near the limits of visibility, the difference in distance which had to exist between two targets before the subjects could see that the targets were not at the same distance, was around ten times as great as in clear water, and much greater than that when compared with performance in air. The decrease in the 'depth acuity' was attributed to the loss of visual cues along the edges of the visual field underwater. The further drop in acuity with increased turbidity of the water was attributed to the loss of relative brightness of the targets. Divers should be made aware that their ability to tell which of two objects is closer to them deteriorates underwater, --increasingly, as the clarity of the water decreases. Performance of divers may be improved, if artificial cues can be provided.

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