Summary
Experiments with subjects of varied diving experience in clear water of Malta showed that divers tend to underestimate the distance of the surface more than that of the seabed. The underestimation is most marked in clear empty water, but disappears with practice. Objects viewed vertically downwards tend to be correctly estimated in size; but this is an underestimate in comparison with the overestimation which normally occurs with horizontal viewing. These effects are similar to the “moon illusion”, but are probably due to visual rather than proprioceptive changes in the vertical plane.
Résumé
Des expériences faites avec des sujets possédant divers niveaux d'expérience de plonger en eau claire devant Malte ont montré ques les plongeurs ont tendance à sous-estimer léloignement de la surface plus que du fond de la mer. Cette sous-estimation se révèle la plus marquée en eau claire et vide, mais disparaît avec l'habitude. Des objets regardés verticalement en bas ont tendance à être estimés justement en grandeur; mais c'est là une sous-estimation en comparaison avec la surestimation qui se produit quand ils sont regardés horizontalement. Ces effets sont semblables à la ≪lune-illusion≫, mais ont probablement pour cause des changements plutôt visuels que proprioceptifs dans le plan vertical.
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Ross, H.E., King, S.R. & Snowden, H. Size and distance judgements in the vertical plane under water. Psychol. Forsch. 33, 155–164 (1970). https://doi.org/10.1007/BF00424982
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DOI: https://doi.org/10.1007/BF00424982