Obstacle avoidance during human walking: learning rate and cross-modal transfer

1. The aim of this study was to investigate the significance of specific af ferent information during motor learning. Blindfolded subjects stepped over an obstacle on a treadmill while different stimuli (acoustic (ACU), somato sensory (SOM) and light flash (LED)) signalled the approaching obstacle. Th e effect of the above stimuli was then evaluated and compared to full visio n (VIS) locomotion. In the non-visual conditions feedback information about the performance was provided by an acoustic signal. 2. Using each of the different stimuli for information the level of subject performance was assessed by noting foot clearance and analysing both leg m uscle electromyographic activity and movement trajectories during three suc cessive runs. Each of these runs consisted of 100 steps over the obstacle. 3. The best performance at the onset of the first run was achieved during t he VIS condition. When the VIS condition (run 1 + 2) was followed by ACU or SOM information or when the ACU condition (run 1 + 2) was followed by LED, little cross-modal transfer (CMT) occurred, i.e. adaptation in run 3 start ed again at a low level of performance. In contrast, if adaptation started with ACU stimuli followed by SOM stimuli, almost full CMT occurred. The abs olute level of performance achieved after the second or third runs was simi lar in the VIS and non-VIS conditions. 4. In conclusion, the course of motor learning depends on specific afferent information, and feedforward control has a special influence on the perfor mance only at the onset of the experiment but not on the rate of learning. The fact that little CMT occurs from visual to nonvisual stimuli and from A CU to LED suggests that visual afferent input is processed in a different w ay to non-visual stimuli.