To duck, or not to duck, that is the question! – Inverse hysteresis effects in a binary full-body task

In sequential motor tasks, people reuse prior motor plans to reduce planning cost, causing a persistence of the prior posture. This persistence, termed motor hysteresis, is indicative of planning efficiency. To date, research on motor hysteresis has focused narrowly on reaching movements. However, hysteresis should also apply to full-body movements if it constitutes a general principle of planning efficiency. To test this, we asked participants to perform a binary full-body posture selection task: going over or ducking under a horizontal bar of varying height. Bar height was varied in ordered sequences to induce hysteresis, and binary decision data was recorded. To ascertain whether full-body tasks could be conducted in a virtual reality (VR) environment without compromising scientific validity, we replicated the task in VR with a second group of participants. Results showed that participants went over lower bar heights and ducked under higher ones. The critical height shifted with order. However, the shift direction indicated an inverse hysteresis effect. This inverse hysteresis was replicated in the second participant group in the virtual environment. Here, participants were more cautious in their decisions and switched to ducking under at lower heights. The similarity of the decision-making behavior across environments lends support to the feasibility of using VR to study full-body movements. Nevertheless, it seems advisable to validate the gained insights in a real environment. The inverse hysteresis effect found in the current study has previously been observed in perception research, where it was interpreted as repetition suppression. Our findings suggest that repetition suppression may also apply to motor planning, particularly when mechanical costs are high, like in full-body movements.