AbstractPeople constantly adapt their movements to changing circumstances; usually relying on their automatic, implicit motor adaptation systems. While the time course of these implicit processes is thought to be slow, there is surprisingly little evidence for this. We tested the effects of various amounts of reach movement feedback on the speed of implicit learning in visuomotor rotation adaptation. Three groups adapted to a 45° rotation: 1) "Continuous", the hand-cursor was continuously visible 2) "Terminal", where a static cursor at the end of each reach gave decreased feedback 3) "Cursor jump", the cursor jumped 45° mid-reach, increasing feedback by introducing the perturbation on each trial. All groups completed the same rotation schedule and alternated their training trials with testing trials: no-cursor reaches with exclusion instructions to probe implicit adaptation. This allowed us to measure the rate of implicit adaptation at a fine temporal resolution. For "terminal" and "cursor-jump" groups, we expect a decrease in the magnitude and possibly rate of implicit adaptation. The training trials showed "continuous" had a higher learning rate with surprisingly less overall adaptation. Testing trials, however, showed more implicit learning for the continuous group and the slowest rate of change. We find that implicit adaptation saturates faster in the "terminal" and slower in the "cursor-jump" condition, compared to "continuous". Our findings show implicit adaptation can be fast and suggests there may be useful feedback-dependent mechanisms which can increase the amount and rate of implicit learning.
Acknowledgments: SD supported by NSERC, DYPH supported by NSERC