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Tracey A. Herlihey, Simon K. Rushton, Cyril Charron; The relationship between perceived straight-ahead and walking direction.. Journal of Vision 2011;11(11):918. doi: 10.1167/11.11.918.
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If an error is injected into the perceptuo-motor loop between the eye and the foot an observer will walk to a target along a curving trajectory. Over time, the trajectory will straighten. Over the same period, the observers' perception of egocentric direction will also change. What is the relationship between the two changes? Does a change, or recalibration, of perceived direction account for the change in trajectory? Our hypothesis was that it does. Specifically we hypothesised that a change in perceived visual direction is responsible for the changes in trajectory. We explored this possibility by injecting a small error into perceived egocentric direction using prisms, and measured trajectory and perception of egocentric direction (visual and proprioceptive) at several time points (after 6, 12 and 24 walking trajectories). In line with our hypothesis, we found that the change in walking trajectory was directly related to the change in perceived visual direction (visual shift), but not felt direction (proprioceptive shift). We were then able to subject our hypothesis to a challenging test: we observed that there appeared to be a marked asymmetry between the visual shifts that resulted from use of leftward displacing prisms and rightward displacing prisms. If our hypothesis was correct, this asymmetry should be reflected in the trajectory data. A corresponding asymmetry in the trajectory data was indeed found. Thus, we conclude that a change in perceived visual direction accounts for the change in trajectory.
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