Kinematics of motor sequence performance in the presence of implicit and explicit structure

Motor sequences can be learnt with or without conscious awareness. Here we investigated how conscious awareness of the sequence structure affects the kinematic characteristics of movements. Two groups of subjects performed either an explicit (simple sequence structure, N=19) or implicit (complex sequence structure, N=12) sequence learning task using KINARM (BKIN Technologies). We found that in both groups, movement parameters were significantly impacted by the sequence structure. In addition, in the explicit group, we observed a clear anticipation of the movements, which allowed movement velocity, and consequently, energy cost, to be spared. In contrast, the pattern of changes observed in the “implicit group” was different, with no anticipation, and affected only a subset of the items within the sequence. This difference between groups could be explained by the fact that movement parameters were influenced by 2 different mechanisms. While the pattern and dynamics of movement parameters in the “explicit group” seemed to be caused by the grouping of successive items into sub-groups, or chunks, the results obtained for the “implicit group” suggest rather the involvement of associative learning mechanisms, whereby statistical regularities are used to predict upcoming targets