Obstacle Crossing: Different Strategies in People with Vision, Blindfolded or Blind

During obstacle crossing, a minimal vertical distance between foot and obstacle (toe clearance) has to be preserved to avoid tripping. This study analyzed the control of an obstacle crossing task as a reaching motion with the foot when visual information was unavailable to blind and sighted participants. A major difference with upper limb reaching is that the lower limb task has to be integrated with the gait task. In this work we will focus on the control of the trajectory of the lower limb end point (the foot) while the base point of the kinematic chain (the hip) is moving over the obstacle. We hypothesized that vision contributes to estimate the body location with respect to the obstacle while proprioceptive information is sufficient to provide adequate toe-clearance. Seven blind and seven sighted participants (with vision available and blindfolded) walked along a flat pathway and crossed the obstacle 30 times as their lower limb kinematics was recorded. Significant differences in the variables related to the hip position and velocity were observed; the relative distance between hip and foot at critical time, normalized to the subject’s height, revealed a distinct behavior between the lack of vision and the vision conditions in both antero-posterior and vertical axes. Results suggest that prolonged lack of vision generates a different strategy to negotiate obstacles. This is a strategy that is probably associated to a lower energy cost.