Prior Uncertainty Impedes Locomotor Adaptation

When walking in a novel environment, experience will influence the initial control mechanisms people select to create stable trajectories. These control mechanisms may enhance or impede the formation of a predictive internal model. Prior exposure to uncertain environments may encourage adaptation of high impedance control strategies to create stable movements and minimize error. Research suggests that adopting an impedance control strategy may accelerate motor learning in a novel and consistent environment by ensuring that actual movements remain close to the planned movement space. Alternatively, control methods that minimize movement errors may limit an important signal for motor learning. Here we examine how prior exposure to environmental uncertainty, pseudorandom perturbations, affects locomotor adaptation to a novel and consistent environment, a laterally directed viscous force field. We find that prior exposure to environmental uncertainty impeded locomotor adaptation to the novel and consistent environment. Participants who experienced prior perturbations made larger movement errors when walking in the viscous force field than participants who did not receive prior perturbations. The greater movement errors among participants who received prior perturbations persisted even after substantial practice in the viscous force field. Participants who experienced prior perturbations selected feedforward strategies that were not predictive of the consistent environment. In addition, participants who received prior perturbations did not make reactive, feedback-driven, adjustments in lateral foot placement in response to the applied viscous force field. The control strategies observed after perturbations were not optimally tuned for the consistent environment and likely imparted additional costs (e.g. metabolic, cognitive). These general control strategies may prioritize stability by enhancing the ability of participants to withstand future unexpected changes in the external environment.

Dr. Keith Gordon