Cutaneous reflex modulation during obstacle avoidance under conditions of normal and degraded visual input

The nervous system integrates visual input regarding obstacles with limb-based sensory feedback to allow an individual to safely negotiate the environment. This latter source can include cutaneous information from the foot, particularly in the event that limb trajectory is not sufficient and there is an unintended collision with the object. However, it is not clear the extent to which cutaneous reflexes are modified based on visual input. In this study, we first determined if phase-dependent modulation of these reflexes is present when stepping over an obstacle during overground walking. We then tested the hypothesis that degrading the quality of visual feedback alters cutaneous reflex amplitude in this task. Subjects walked and stepped over an obstacle-leading with their right foot-while we electrically stimulated the right superficial peroneal nerve at the level of the ankle at different phases. Subjects performed this task with normal vision and with degraded vision. We found that the amplitude of cutaneous reflexes varied based on the phase of stepping over the obstacle in all leg muscles tested. With degraded visual feedback, regardless of phase, we found larger facilitation of cutaneous reflexes in the ipsilateral biceps femoris-a muscle responsible for flexing the knee to avoid the obstacle. Although degrading vision caused minor changes in several other muscles, none of these differences reached the level of significance. Nonetheless, our results suggest that visual feedback plays a role in altering how the nervous system uses other sensory input in a muscle-specific manner to ensure safe obstacle clearance.