Judging beforehand the possibility of passing under obstacles without motion: the influence of egocentric and geocentric frames of reference |
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Authors: | L Bringoux G Robic G M Gauthier J L Vercher |
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Institution: | (1) UMR CNRS 6152 “Mouvement & Perception”, Faculté des Sciences du Sport, Université de la Méditerranée, 163, avenue de Luminy CP 910, 13288 Marseille Cedex 9, France |
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Abstract: | Previous studies have shown that the perception of the earth-based visual horizon, also named Gravity Referenced Eye Level
(GREL), is modified by body tilt around a trans-ocular axis. Here, we investigated whether estimates of the elevation of a
luminous horizontal line presented on a screen in otherwise darkness and estimates of the possibility of passing under are
identically related to body tilt in absence of motion. Results showed that subjects overestimated the elevation of the projected
line, whatever their body orientation. In the same way, subjects also overestimated their capacity of passing under the line.
Both estimates appeared as a linear function of body tilt, that is, forward body tilt yielded increased overestimations, and
backward body tilt yielded decreased overestimations. More strikingly, the linear effect of body tilt upon these estimates
is comparable to that previously observed for direct GREL judgements. Overall, these data strongly suggest that the perception
of the elevation of a visible obstacle and the perception of the ability of passing under in otherwise darkness shared common
processes which are intimately linked to the GREL perception. The effect of body tilt upon these perceptions may illustrate
an egocentric influence upon the semi-geocentric frame of reference required to perform the task. Possible interactions between
egocentric and geocentric frames of reference are discussed. |
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Keywords: | Spatial perception Egocentric Geocentric Frame of reference Gravity Referenced Eye Level Body orientation |
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