Predictability of trajectory modulates manual tracking: from real-time feedback to internal-model-based control.

We humans manifest a remarkable capability of adapting to varying external environments. However, investigations into mechanisms that enable such adaptations raise several fundamental questions in the domain of sensorimotor control-most notably, whether and how we employ internal representations to facilitate more efficient feedforward control. The current study addressed this question by examining how trajectory predictability modulates manual tracking in human participants. A somewhat surprising finding was that no significant improvement was observed in tracking performance due to predictability, regardless of whether people were aware of it. However, analyses using a Kalman filter model revealed that participants did adapt their visuomotor processes by reducing their reliance on real-time visual input when tracking more predictable trajectories. These results suggest that, despite seemingly comparable tracking performances, participants increasingly relied on internal control mechanisms rather than real-time inputs when confronted with higher trajectory predictability. This study provides new insights into human sensorimotor control, highlighting adaptive use of information redundancy from the environments and the balance between feedforward and feedback mechanisms of human beings.