Online reach adjustments induced by real-time movement sonification

Paper Abstract: Movement sonification is the real-time conversion of sensor readings of body motion into acoustic feedback. Such acoustic feedback can improve motor learning in healthy subjects (e.g., learning a new sport skill) and those with sensorimotor deficits (e.g., stroke patients and those suffering from deafferentiation). However, motor learning involves both developing feedforward inverse internal models for planning motor trajectories and developing a capacity to correct erroneous trajectories in real-time via online feedback control. This latter motor-control perspective has not been well-studied in movement sonification research and it is not known whether motor learning improvements from movement sonification are driven by improved inverse internal models, corrective real-time adjustments, or both. We searched for evidence of real-time adjustments (muscle twitches) in response to movement sonification by comparing the kinematics of reaches made with online and terminal sonification feedback. We found that reaches made with online feedback were significantly more jerky than reaches made with terminal feedback, indicating increased muscle twitching. Using a between-subject design, we found that online feedback was associated with improved motor learning of a reach path and target over terminal feedback; however, using a within-subjects design, we found that switching participants who had learned with online sonification feedback to terminal feedback was associated with a decrease in error. Thus, our results suggest that, with our task and sonification, movement sonification leads to online motor adjustments which improve motor trajectory planning, but which themselves are not helpful online corrections.