Where do we look when we walk on stairs? Gaze behaviour on stairs, transitions, and handrails.

Stair walking is a challenging locomotor task, and visual information about the steps is considered critical to safely walk up and down. Despite the importance of such visual inputs, there remains relatively little information on where gaze is directed during stair walking. The present study investigated the role of vision during stair walking with a specific focus on gaze behaviour relative to (1) detection of transition steps between ground level and stairs, (2) detection of handrails, and (3) the first attempt to climb an unfamiliar set of stairs. Healthy young adults (n = 11) walked up and down a set of stairs with 7 steps (transitions were defined as the two top and bottom steps). Gaze behaviour was recorded using an eye tracker. Although participants spent most part of the time looking at the steps, gaze fixations on stair features covered less than 20% of the stair walking time. There was no difference in the overall number of fixations and fixation time directed towards transitions compared to the middle steps of the stairs. However, as participants approached and walked on the stairs, gaze was within 4 steps ahead of their location. The handrail was rarely the target of gaze fixation. It is noteworthy that these observations were similar even in the very first attempt to walk on the stairs. These results revealed the specific role of gaze behaviour in guiding immediate action and that stair transitions did not demand increased gaze behaviour in comparison with middle steps. These findings may also indicate that individuals may rely on a spatial representation built from previous experience and/or visual information other than gaze fixations (e.g. dynamic gaze sampling, peripheral visual field) to extract information from the surrounding environment.