Sensorimotor adaptation to sustained lower visual field occlusion during continuous locomotion with and without obstacle negotiation.

The importance of having visual feedback of the lower-limb to locomotion control, has typically been examined by intermittently occluding the lower visual field (lvf) in repeated obstacle crossing trials. A consistent finding is that foot clearance increases following lvf occlusion. However, there is some evidence that the increase in clearance diminishes with further repetition. This calls into question the importance of lvf feedback in the control of locomotion. We present two studies investigating how foot clearance is affected as a result of sustained lvf occlusion during continuous locomotion over i) a level surface and ii) the same surface, but involving intermittent obstacle negotiation. In both studies, clearance increased following lvf occlusion but then diminished within a few minutes of continued walking: suggesting that the initial increase may have been an acute but transient response. After four minutes, clearance in level-walking had returned to pre-occlusion levels, whereas for obstacle crossing, clearance remained elevated and showed only a slight lessening over time. These findings provide support for the notion that lvf ex-proprioceptive information is not paramount in the control of the swinging limb/foot during overground gait, but it is customarily used in adaptive gait involving obstacle crossing in determining foot placement before the obstacle and hence clearance over it. We argue that lvf occlusion leads to a more general 'acute' perturbation of gait that is not necessarily related to the elimination of visual ex-proprioceptive feedback, and this has implications for the design of laboratory-based studies investigating the role of vision in locomotion.