Non-Linear Extrapersonal Space: An Additional Twist in Prism Adaptation K Pochopien1, T Stemmler2, K Spang1, M Fahle1 |
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1Human Neurobiology, University of Bremen, Germany |
| Prisms can shift the visual world laterally. In experiments, subjects usually have to point to a central target, seen - due to the prism shift - in the near periphery of the visual field. Pointing errors decrease due to neuronal shifts: adapted, subjects either perceive the peripheral visual direction as straight ahead or change their arm proprioception for straight-ahead towards the perceived target location. Hence, visual and haptic adaptation involve opposite directions from different starting points, but are usually supposed to add linearly due to a linear spatial representation. We tested this assumption by asking subjects to point to targets both centrally and in peripheral space without visual feedback, both before and after prism adaptation. Without visual feedback: a) subjects consistently underestimate the amount of eccentricity, i.e. perform movements too close to the center even before prism adaptation; b) over the course of ten movements these movements shift even closer to the center; c) prism adaptation increases this effect: observers adapt to the position of a target during prism adaptation but underestimate the eccentricity of peripheral targets even more than before adaptation. We conjecture that the adaptation process underlying prism adaptation changes space representation in a complex and “conservative” way. |
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