Prism Adaptation: Why is it so difficult to understand? M Fahle1, T Stemmler2, C Grimsen1, K Spang1 |
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1Human Neurobiology, University of Bremen, Germany |
| When we put on prisms shifting the visual world laterally, we usually need only a few movements to almost perfectly adapt to them. After removing the prisms, our movements deviate initially in the opposite direction, a nice after-effect lasting almost as long as the adaptation process. All that seems to be required for adaptation is a lateral shift, in the nervous system, neutralizing the optic shift induced by the prisms. But prism adaptation, contrary to intuition, is a purely proprioceptive effect: the proprioceptive signals of the eye, neck or arm have to be adapted, while the visual input stays identical, due to compensatory eye movements. We measured these three adaptations separately for the subjective straight ahead of eyes, head, and arm without visual feedback (in the dark). It turns out that the relative amount of adaptation depends on various factors such as the amount of visual feedback (full arm movement seen versus feedback only at endpoint of movement), presence of additional acoustic feedback, target position in the visual field, angle between arm and trunk, type of movement, and even inter-individual differences. These dependencies explain differences in reported results, for example some studies reporting transfer between arms while others do not. |
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