Adaptation of Divers to Size Distortion Under Water

Abstract

A diver's face-mask produces an optical distortion of the relationship between size and distance under water, with the result that objects normally appear further than the optical distance and enlarged. Adaptation to size enlargement was examined by obtaining size estimates in air and water, before and after a period of 20-40 min. underwater activity in which objects of known size were handled. Size estimates were obtained by adjusting a line to an est,imated length of 12 in. Initial estimates in water indicated that novices experienced more size enlargement than experienced divers. Both groups of divers showed significant aftereffects in air, indicating that some size adaptation had occurred. The aftereffect declined rapidly, and was significant for only the first two trials. A second experiment showed that the greater accuracy of experienced divers also occurred when looking into water through a porthole: it was not, therefore, 'situationcontingent' in the sense that it depended upon wearing a face-mask in water.

Investigation of vibrational characteristics of composite beams with fluid–structure interaction

“…According to Ref. [15], the degree to which the composite beam is magnified can be calculated using the following equation:…”

Underwater Work Measurement Techniques

“…That is, some subjects improved their judgments of size by degrading their judgments of distance and some the other way around. (References 10,16,18,19).…”

Why do objects appear enlarged under water?

“…In general the overestimation was very much less than the angular magnification of 1.33, and also much less than would be predicted from the distance judgements according to classical SDI. The discrepancy may have been caused by the methods of measurement, or by previous perceptual learning on the part of more experienced divers, or to rapid adaptation during the course of the measurements (10,(13)(14) . However, the results might be consistent with perceptual SDI, if the perceived angular size was less than the optical magnification (Figure 2b).…”

“…1.35* 4) Ross et al (13) Manual adjustment 1.19 -(remembered size) 5) Kinney & Luria (16) Disc selection 1.25 -(remembered size) 6) Goeters (17) Manual adjust.…”