ABSTRACT
Contemporary theories of motor control have suggested that multiple motor commands compete for action selection. While most of these competitions are completed prior to movement onset, averaged saccadic eye movements that land at an intermediate location between two visual targets are thought to arise when a movement is initiated prior to the resolution of the competition. In contrast, while averaged reach movements have been reported, there is still debate on whether averaged reach movements are the result of a resolved competition between two potential actions or a strategic behavior that optimally incorporates the current task demands. Here, we use a reach version of the paradigm that has previously shown to elicit saccadic averaging to examine whether similar averaging occurs based on neuromuscular activity of an upper limb muscle. On a single trial basis, we observed a temporal evolution of the two competing motor commands during a free-choice reach task to one of two visual targets. The initial wave of directionally-tuned muscle activity (∼100 ms after target onset) was an averaged of the two motor commands which then transformed into a single goal-directed motor command at the onset of the voluntary reach (∼200-300 ms after target onset). The transition from an early motor command to a single goal-direct command resembled the fact that saccadic averaging was most prominent for short-latency saccades. Further, the idiosyncratic choice made on a given trial was correlated with the biases in the averaged motor command.
