Abstract
If the adaptive mechanisms to prism-induced lateral deviation have been widely investigated, little is known about prism-induced alteration of distance. The purpose of the present experiment was to study if a similar pattern of visuomotor plasticity applies to a prism-induced distortion of distance. The experimental paradigm involved successively pre-test measures, an exposure phase and post-test measures. The adaptation process was evidenced by a compensatory aftereffect between the pre- and post-tests. During the exposure, subjects had to point quickly to a visual target with their left hand seen through a pair of 5 Δ base-out prisms spectacles. Visuomotor adaptation was assessed by open-loop pointing (i.e. without seeing the hand) to visual targets with the left (exposed) hand. Visual adaptation (an adaptive process common to all effectors) was assessed by open-loop pointing to visual targets with the right (unexposed) hand. Proprioceptive adaptation of the left hand was measured by pointing to the left hand with the right hand while blindfolded. Motor adaptation of the left hand was indirectly inferred by calculating the difference between the visuomotor aftereffect and the algebraic sum of the visual and proprioceptive aftereffects. A significant aftereffect was obtained for both visuomotor and visual components. No aftereffect was found for the proprioceptive component. The fact that the visuomotor aftereffect was significantly greater than the sum of the visual and (null) proprioceptive aftereffects is an indication that a motor adaptation had developed during exposure in addition to a visual adaptation. These findings highlighted short-term adaptive components to prism-induced distortion of distance. The adaptive components differed from those found with prism-induced lateral deviation by their respective contributions to the aftereffect, the latter ones involving little visual adaptation. Such differences in visuomotor adaptation may be attributed to the accuracy of the available error signals, and could rely on different levels of plasticity.
Grant N° 07CO802 from Délégation Générale pour l'Armement