Abstract
The aim of this study was to investigate the visual control strategies that walkers use to step over obstacles, with a specific focus on how the adopted strategy allows walkers to accommodate variations in obstacle height and depth. Subjects walked through a virtual environment viewed through a head-mounted display while their lower body was tracked by a motion capture system. They walked from a home position to a goal while stepping over a virtual obstacle, the height and depth of which were manipulated as independent variables. We found that adaptations to variations in obstacle dimension began during the step by the trailing foot to its location in front of the obstacle. Subjects adapted to deeper obstacles by planting their trailing foot closer to the obstacle, which allowed the leading foot to reach peak elevation closer to the intended landing location behind the obstacle. However, planting the trailing foot closer to the obstacle means that it must be elevated more quickly as it moves forward to clear deeper obstacles. The trailing foot must be elevated more quickly to clear taller obstacles as well. To maintain stability and forward progress while quickly elevating the trailing foot, walkers could lean the upper body forward toward the end of the leading foot's step over deeper and taller obstacles, and then let the upper body return to equilibrium as the trailing foot is rapidly lifted to clear the obstacle. This is consistent with an observed decrease in head velocity while the trailing foot crosses the obstacle. We test this hypothesis in a follow-up experiment in which walkers step over different sized obstacles with their right and left feet. The findings suggest that visual information about obstacle dimension is used to modulate stepping behavior as early as the last step before the obstacle.
Meeting abstract presented at VSS 2014