Coexistence of two adaptation processes in a visuomotor rotation task

Motor adaptation is a learning process that enables humans to regain proficiency when sensorimotor conditions are sustainably altered. Many studies have documented the properties of motor adaptation, yet the underlying mechanisms of motor adaptation remain imperfectly understood. In this study, we propose a computational analysis of adaptation to a visuomotor rotation task and examine it through an experiment. Our analysis suggests that two distinct processes contribute to produce adaptation: one which straightens trajectories, and another which redirects trajectories. We designed a visuomotor rotation task in a three-dimensional (3-D) virtual environment where human participants performed a pointing task using a head-mounted display controller represented by a cursor that was visually rotated by an angular deviation relative to its actual position. We observed that: <i>1</i>) the trajectories were initially curved and misdirected, and became straighter and better directed with learning; <i>2</i>) the straightening process occurred faster than the redirection process. These findings are consistent with our computational analysis and disclose a new and different perspective on motor adaptation.<b>NEW & NOTEWORTHY</b> This study investigates the visuomotor rotation protocol using a pointing task to compare the adaptation of <i>1</i>) the movement initial angle, <i>2</i>) the trajectory length. The experiment shows that these two outcomes adapt on different time scales. To account for this observation, we propose a computational analysis based on the control-estimation framework.