Spatial and temporal gaze decisions during walking: role of uncertainty, task priority, and motor cost

We continuously use vision to navigate the cluttered environment in which we live. To accomplish this, we adapt the location and timing of gaze shifts to gain environmental information to achieve a behavioural goal. However, despite the growing interest in eye tracking research during natural behaviours, the factors that guide gaze behaviour to accurately navigate and interact with our environment still remain unclear. The goal of this thesis is to determine the relationship between environmental, cognitive, and biomechanical factors in the control of gaze during visually-guided walking. In the first study, I sought to understand how environmental uncertainty influences gaze behaviour to accurately perform a motor action. To test this, I used a visually-guided walking task where I manipulated the visual uncertainty associated with stepping targets. Using different task instructions to manipulate the value assigned to foot-placement accuracy, I found that environmental uncertainty increases gaze time on visual targets when having to step accurately. In the second study, I tested if motor cost, a factor that influences the way we move, is integrated into the decision of when to shift gaze to upcoming stepping targets. I found that the cost associated with redirecting foot placement onto a target modifies how gaze is allocated; when the cost to move the body increases, gaze strategies shift from one that focuses on the planning of future steps to one that prioritizes online visual control of the current action. After identifying how uncertainty, motor cost, and task priority influence gaze behaviour, in the third study, I aimed to understand how these factors interact to decide where to look when facing multiple choices for foot placement. Using a forced-choice walking paradigm, I showed that when facing a decision conflict, where two targets compete for gaze allocation, people sample the environment using different strategies that lead to differences in walking decisions. This suggests that, during walking, individuals assign a different priority to information and motor cost. Taken together, my thesis provides a novel perspective on the factors that guide gaze strategies during walking.