Rotation size drives heterogeneous explicit strategy development in motor adaptation

Visuomotor adaptation typically involves an interplay between implicit and explicit processes. While explicit strategy development has often been characterized as an exponential function, recent work has shown that individual participants usually show different time courses. Here we identify 3 styles of explicit strategy development and test how these rely on rotations ranging from 20{degrees} to 60{degrees}. Participants self-reported their planned reach direction, allowing us to record a trial-by-trial strategy development time course. We used machine learning to determine the start and stabilization of strategy development. We then use descriptive statistics of this phase to cluster participants into stepwise, gradual, and exploratory strategy learning styles. First, larger rotations increased the proportion of participants who spontaneously developed a strategy. Crucially, the proportions of strategy learning styles also varied as a function of perturbation size; larger rotations (50{degrees}-60{degrees}) favored exploratory and stepwise strategies, whereas smaller rotations (20{degrees}-30{degrees}) predominantly yielded gradual learning, with no exploratory behaviour observed in the 20{degrees} group. These findings challenge the notion of explicit adaptation as a homogeneous process. They also suggest that rotation size may boost non-gradual strategy formation.