Force control in the absence of visual and tactile feedback.

Motor control tasks like stance or object handling require sensory feedback from proprioception, vision and touch. The distinction between tactile and proprioceptive sensors is not frequently made in dynamic motor control tasks, and if so, mostly based on signal latency. We previously found that force control tasks entail more compliant behavior than a passive, relaxed condition and by neuromuscular modeling we were able to attribute this to adaptations in proprioceptive force feedback from Golgi tendon organs. This required the assumption that both tactile and visual feedback are too slow to explain the measured adaptations in face of unpredictable force perturbations. Although this assumption was shown to hold using model simulations, so far no experimental data is available to validate it. Here we applied a systematic approach using continuous perturbations and engineering analyses to provide experimental evidence for the hypothesis that motor control adaptation in force control tasks can be achieved using proprioceptive feedback only. Varying task instruction resulted in substantial adaptations in neuromuscular behavior, which persisted after eliminating visual and/or tactile feedback by a nerve block of the nervus plantaris medialis. It is concluded that proprioception adapts dynamic human ankle motor control even in the absence of visual and tactile feedback.