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Heather Jenkin, James Zacher, Richard Dyde, Laurence Harris, Michael Jenkin; How do SCUBA divers know which way is up? The influence of buoyancy on orientation judgements. Journal of Vision 2009;9(8):716. doi: 10.1167/9.8.716.
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© 2015 Association for Research in Vision and Ophthalmology.
One's perception of the direction of up is influenced by a number of cues including the nature of the visual display (visual cues), the orientation of the body (idiotropic cues), and gravity (gravity cues). Normally these cues exist in close agreement, but in unusual environments, including underwater and outer space, these cues may be placed in conflict and some cues may not be available at all. NASA uses underwater training to give astronauts a sense of reduced gravity cues as being underwater cancels many body cues to orientation while leaving the otolith-transduced cue unaltered. SCUBA divers report re-orientation illusions when underwater especially when visual cues to orientation are reduced. Here, we investigate how advanced SCUBA divers integrate visual, idiotropic and gravity cues to orientation. Perception of self-orientation was measured using the Oriented Character Test (OCHART, see Dyde et al., 2006). OCHART requires observers to recognize an oriented character (here the letter “d” as either a “p” or a “d” as it is presented in different orientations). Divers viewed the OCHART probe through an underwater window at approximately 4′ depth. Each OCHART session consisted of 672 trials; four different visual backgrounds, 24 different character orientations, and seven repetitions. The influence of the body's orientation was manipulated by having divers assume two different orientations while completing these tasks: (1) right-side down and (2) upright. Observers performed the task both in and out of the water. Divers in a right side down orientation showed a reduced reliance on visual cues underwater compared to performance on dry land, revealing a decrease in the visual effect on average. This finding is consistent with results from short duration parabolic flights where a reduced reliance on visual cues is also found (http://journalofvision.org/6/6/183/).
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