Abstract
One persistent curiosity in visuomotor adaptation tasks is the fact that participants often reach a learning asymptote well below full compensation. This incomplete asymptote has been explained as a consequence of obligatory computations in the implicit adaptation system, such as an equilibrium between learning and forgetting. A body of recent work has shown that in standard adaptation tasks, cognitive strategies operate alongside implicit learning. We reasoned that incomplete learning in adaptation tasks may primarily reflect a speed-accuracy tradeoff on time-consuming motor planning. Across three experiments, we find evidence supporting this hypothesis, and demonstrate that the incomplete asymptote of adaptation appears to be primarily a consequence of hastened motor planning. When an obligatory waiting period was administered before participants executed their movements, they were able to fully counteract imposed perturbations (experiment 1). Inserting the same delay between trials - rather than during movement planning - did not induce full compensation, suggesting that motor planning time predicts the learning asymptote (experiment 2). In the last experiment, instead of directly manipulating the planning time, we asked participants to continuously report their movement aim. We show that emphasizing explicit re-aiming strategies also leads to full asymptotic learning, supporting the idea that prolonged motor planning may involve a parametric rotation of aiming direction whose premature termination yields incomplete asymptotic learning (experiment 3). Findings from all experiments support the hypothesis that incomplete adaptation is, in part, the result of an intrinsic speed-accuracy tradeoff, perhaps related to cognitive strategies that require parametric attentional reorienting from the visual target to the goal.
