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Prism adaptation: Dependency on motion trajectory


Cunningham,  DW
Department Human Perception, Cognition and Action, Max Planck Institute for Biological Cybernetics, Max Planck Society;

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Munka, L., Kaernbach, C., & Cunningham, D. (2002). Prism adaptation: Dependency on motion trajectory. Poster presented at 5. Tübinger Wahrnehmungskonferenz (TWK 2002), Tübingen, Germany.

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In order to pick up an object, its visual location must be converted into the appropriate motor commands. Introducing a discrepancy between the seen and felt location of the object (e.g., via prism goggles) initially impairs our ability to touch it. The sensory systems rapidly adapt to the discrepancy, however, returning perception and performance to near normal. Subsequent removal of the discrepancy leads to a renewed performance decrement -- a Negative Aftereffect (NAE). It is generally believed that this adaptation consists primarily of “recalibrating” the transformation between the visual and proprioceptive perception of spatial location (Bedford, 1999). According to such a purely perceptual account of adaptation, the exact path used to reach the object should not be important. If, however, it is the transformation from perception to action that is being altered, then changing the motion trajectory should reduce or eliminate the NAE. Starting with both hands on the desktop, the chin resting on a horizontal bar, participants (N=72) had to touch a cross presented at eye level on a touch screen 30 cm in front of them. Four trajectories were possible: reaching to the cross from below or (swinging the arm backwards) from above the bar, using either their left or their right hand. Reaching Accuracy without feedback was determined for all four trajectories before and after adaptation to a single trajectory with prism goggles (19° horizontal displacement). The NAE was 46mm (8.7°) for the adapted trajectory, 26mm negligable for both trajectories of the other hand. The NAE was larger for unfamiliar (above bar, or usage of non-preferred hand) than for familiar trajectories. Visuomotor adaptation is not merely a perceptual recalibration. Not only does the structure of the motion trajectory play a central role, but the familiarity of the trajectory also seems to be important. These results have strong implications for all models of visuomotor adaptation.