Enhancing memory of stair height by the motor experience of stepping.

A concept emerging from recent studies on obstacle avoidance in quadrupeds is that working memory of the height of an obstacle established by visual information is enhanced by motor interactions with the obstacle. In this investigation, we found that this concept is valid in adult humans when viewing and walking up stairs. The main finding was that the memory of the height of stairs was enhanced when information about stair height was gained by walking up a short flight of stairs compared to when information about stair height was gained by vision alone. By measuring the maximum toe clearance when subjects step onto a stair, we observed that maximum toe clearance increased after diverting vision from the stair for a few seconds prior to stepping. Most of this increase occurred within a 2-s period between diverting vision from the stair and initiating the step. By contrast, this increase in maximum toe clearance after diverting vision from a stair was significantly reduced after subjects walked up two stairs prior to stepping onto a stair without vision. This reduction persisted for delays as long as 10 s between diverting vision from the stair and initiating the step. In four of twelve subjects, the maximum toe clearance after these long periods without vision of the stair was close to the value when steps were made with full vision of the stairs.