Detection Thresholds for Replay and Real-Time Discrepancies in VR Hand Redirection

Hand redirection, which subtly adjusts a user's hand movements in a virtual environment, can modify perception and movement by providing real-time corrections to motor feedback. In the context of motor learning and rehabilitation, observing replays of movements has been shown to enhance motor function. The application of hand redirection to these replays by making movements appear larger or smaller than they actually are has the potential to improve motor function. However, the detection threshold for hand redirection, specifically in the context of motion replays, remains unclear, as it has primarily been studied in real-time feedback settings. This study aims to determine the threshold at which hand redirection during post-exercise replay sessions becomes detectable. We conducted two psychophysical experiments to evaluate how much discrepancy between replayed and actual movements can go unnoticed by users, both with hand redirection (N=20) and without (N=18). Our findings reveal a tendency for the amount of movement during replay to be underestimated. Furthermore, compared to conventional real-time hand redirection without replay, replay manipulations involving redirection applied during the preceding reaching task resulted in a significantly larger JND. These insights are crucial for leveraging hand redirection techniques in replay-based motor learning applications.