Online and offline contributions to recently acquired reaching movements

Abstract

The use of sensory feedback for online and offline movement corrections has been widely studied for well learned actions, but not for actions in a novel visuomotor environment. We asked if the contributions of online and offline motor control differ between recently acquired reaching movements from well learned reaching. Eight participants were divided into 2 groups, one receiving continuous visual feedback during all reaches (CF), and another receiving terminal feedback regarding movement endpoint (TF). Participants then trained in a visuomotor environment by reaching to 3 targets when (1) a cursor accurately represented their hand motion and (2) a cursor was rotated 45 degrees clockwise relative to their hand motion. After training in each visuomotor environment, contributions were then probed by having participants complete 4 blocks of reaches with constrained reaction time (RT) and movement time (MT) (SlowRT-SlowMT, SlowRT-FastMT, FastRT-SlowMT and FastRT-FastMT). Participants demonstrated similar performance (i.e. MT and angular errors) regardless of feedback or reaching environment during training. Once constraints were imposed, offline control measures (i.e., squared Fisher z) indicated that early movement positions were more predictive of movement end point when reaching with a rotated cursor compared to an aligned cursor for both groups. Alternatively, online control measures (i.e., time to peak velocity and jerk score) did not differ for reaches completed with aligned or rotated feedback for either group. Together, these results suggest a greater contribution of offline control processes when reaching in a novel visuomotor environment compared to when reaching in a well learned environment.

Acknowledgments: Supported by the Natural Sciences and Engineering Research Council of Canada (NSERC); awarded to the last author.