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Bing Wu, Roberta L. Klatzky; Spatial updating of locations after posture changes in the vertical dimension. Journal of Vision 2005;5(8):200. doi: 10.1167/5.8.200.
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© ARVO (1962-2015); The Authors (2016-present)
A large body of research has focused on spatial updating after rotational and/or translational motions on the ground. Here we extend the research into the third dimension: How good is updating of spatial representation after body movements in the vertical dimension, such as posture changes (e.g., sitting to standing)? Underlying this work is the assumption that when people update spatial location after shifts in posture, they center their spatial coordinate system on some self-referred location. The body and head are candidates for such ego-centers and indeed, both may be present and interact in spatial updating. The first experiment tested the hypothesis that people use shift in perceived eye level to update their vertical position after a postural change. It examined the perception of eye level in different postures and also directly measured judgments of relative shift in eye level across postural changes. To assess the relative effectiveness of visual cues and vestibular/proprioceptive cues, subjects were tested in both dark and lit environments. The experiment found that eye level was perceived with reasonable accuracy in the light, but underestimated by a similar amount across all postures in the dark. Thus judging eye-level shift from the difference in perceived eye levels would have led to accurate responses. In contrast, the relative shift was over-perceived in both lit and dark conditions. An ongoing experiment is testing whether updating of body position leads to commensurate change in head posture, so as to maintain gaze. Subjects in light or dark are asked to maintain eye fixation on a previously viewed target as accurately as possible while sitting down or standing up. Their head orientation is continuously tracked to determine whether there is slippage between body and head change. Errors will be related to the corresponding errors from Experiment 1, to test whether slippage in gaze and misperception of eye-level shift stem from a common origin.
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