Gaze shifts during dual-tasking stair descent

Gaze shifts during dual‑tasking stair descent Veronica Miyasike‑daSilva 0 1 2 William E. McIlroy 0 1 2 0 Heart and Stroke Foundation Canadian Partnership for Stroke Recovery, Sunnybrook Health Sciences Centre , Toronto , Canada 1 Department of Kinesiology, University of Waterloo , Waterloo , Canada 2 Center for Physical Ergonomics, Liberty Mutual Research Institute for Safety , 71 Frankland Road, Hopkinton, MA 01748 , USA 3 Veronica Miyasike-daSilva To investigate the role of vision in stair locomotion, young adults descended a seven-step staircase during unrestricted walking (CONTROL), and while performing a concurrent visual reaction time (RT) task displayed on a monitor. The monitor was located at either 3.5 m (HIGH) or 0.5 m (LOW) above ground level at the end of the stairway, which either restricted (HIGH) or facilitated (LOW) the view of the stairs in the lower field of view as participants walked downstairs. Downward gaze shifts (recorded with an eye tracker) and gait speed were significantly reduced in HIGH and LOW compared with CONTROL. Gaze and locomotor behaviour were not different between HIGH and LOW. However, interindividual variability increased in HIGH, in which participants combined different response characteristics including slower walking, handrail use, downward gaze, and/or increasing RTs. The fastest RTs occurred in the midsteps (non-transition steps). While gait and visual task performance were not statistically different prior to the top and bottom transition steps, gaze behaviour and RT were more variable prior to transition steps in HIGH. This study demonstrated that, in the presence of a visual task, people do not look down as often when walking downstairs and require minimum adjustments provided that the view of the stairs is available in the lower field of view. The middle of the stairs seems to require less from executive function, whereas visual attention appears a requirement to detect the last transition via gaze shifts or peripheral vision. Stair locomotion; Vision; Gaze behaviour; Dual task Introduction Humans rely on vision to successfully interact with the surrounding environment. The role of vision in the control of movement is well documented for upper limb movements (Servos and Goodale 1994; Aglioti et al. 1995; Land et al. 1999) and for locomotion (Patla and Vickers 1997; Mohagheghi et al. 2004) , with much of this work focussed on the role of foveal or central vision. Yet, for locomotor behaviours, the peripheral visual field may be particularly important given the relevant visual information available in a wide range of the field of view (Graci et al. 2010; ReedJones et al. 2014). However, in locomotor tasks requiring precise stepping, such as in stair navigation, the requirements for higher-resolution visual inputs have influenced research to focus on the role of foveal visual information for detection of stair physical properties (e.g. step rise and run). This emphasis on foveal vision may have led to an underestimation of the role of peripheral vision during locomotion. Additionally, peripheral vision appears to have an important role even for target behaviours during stair walking, such as grasping of handrails (King et al. 2010; Miyasike-daSilva et al. 2011) . In the present study, we explored the role of foveal and lower field of view information during the task of navigating stairs. Previous studies have revealed the importance of vision on stair climbing (Zietz and Hollands 2009; MiyasikedaSilva et al. 2011) . Nevertheless, foveal fixations directed to stair features (e.g. steps, handrails) decrease when individuals are engaged in a concurrent visual task with little impact on locomotor behaviour (Miyasike-daSilva and McIlroy 2012) . This decrease in foveal fixations suggests that peripheral vision is able to “capture” sufficient information about the spatial and physical properties of the stairs relative to the lower limbs required to guide stair walking. If so, a condition for using information from the peripheral visual field would be an optimal line of gaze to allow extraction of visual information from the extrafoveal visual field. The reliance on peripheral visual field information would provide additional advantages including minimizing the need to scan large field of view with foveal vision and releasing foveal vision to engage in other tasks. In the current study, we sought to advance our fundamental understanding of the specific role of foveal vision during locomotion. We used a dual-task paradigm in which visual task conditions challenged the use of foveal vision and the associated peripheral vision to control stair locomotion. The specific point of gaze required to perform the visual task permitted measurement of timing and frequency of gaze shifts to probe the dependence on lower peripheral visual information to control stair walking. For instance, a line of gaze directed forward could limit the view of the stair in the periph (...truncated)