Motor cost affects the decision of when to shift gaze for guiding movement

Abstract

Frequent gait modifications are often required to navigate our world. These can involve long or wide steps or changes in direction. People generally prefer to minimize the motor cost (or effort) of a movement, although with changes in gait this is not always possible. The decision of when and where to shift gaze is critical for controlling motor actions, since vision informs the brain about the available choices for movement—in this case, where to step. Here we asked how motor cost influences the allocation of gaze. To address this, we had participants walk and step to the center of sequential targets on the ground. We manipulated the motor cost associated with controlling foot placement by varying the location of one target in the lateral direction on a trial-to-trial basis within environments with different numbers of targets. Costlier steps caused a switch from a gaze strategy of planning future steps to one favoring visual feedback of the current foot placement when participants had to negotiate another target immediately after. Specifically, costlier steps delayed gaze shifts away from the manipulated target. We show that this relates to the cost of moving the leg and redirecting the body’s center of mass from target to target. Overall, our results suggest that temporal gaze decisions are affected by motor costs associated with step-to-step demands of the environment. Moreover, they provide insight into what affects the coordination between the eyes and feet for the control of stable and accurate foot placement while walking. NEW & NOTEWORTHY Changes in gait allow us to navigate our world. For instance, one may step long or wide to avoid a spilled drink. The brain can direct gaze to gather relevant information for making these types of motor decisions; however, the factors affecting gaze allocation in natural behaviors are poorly understood. We show how the motor cost associated with a step influences the decision of when to redirect gaze to ensure accurate foot placement while walking.

Effort-based decision-making and gross motor performance: Are they linked?

“…First, planning rather than decision-making may have been the cognitive construct that governed our gross motor task. Some researchers characterize planning as a part of decisionmaking in the context of gross motor performance (9,26,27). However, for gross motor performance, decision-making may align with deciding whether or not to perform a task (i.e., "taking action") or selecting from multiple ways to perform a task (9) rather than monitoring the performance of the task (i.e., matching steps to a metronome beat) (23).…”

“…However, for gross motor performance, decision-making may align with deciding whether or not to perform a task (i.e., "taking action") or selecting from multiple ways to perform a task (9) rather than monitoring the performance of the task (i.e., matching steps to a metronome beat) (23). Planning and decisionmaking may also have occurred serially rather than simultaneously (19,27,28) in our task: participants may have planned when to make initial heel contact prior to beginning the actual movement (14)(15)(16)(17). Thus, the neurological substrates involved in deciding on versus monitoring gross motor performance may be different (18,(29)(30)(31).…”

“…We intentionally omitted feedback to participants because we wanted to assess whether a relationship existed between effort-based decision-making and gross motor performance during a task that was purely focused on motor processes and because we thought that including the constraint to meet the metronome pace would transform walking into a complex, goal-oriented task (9,37) rather than the task of walking with no constraint (38,39). It could be that effort-based decision-making and motor performance are more likely to intersect when an error in achieving a goal is perceived as in the introduction of a perturbation (9) or in relation to the cost of making an error (27,40). Future studies will examine possible links between decision-making and gross motor performance in the presence of a reward and with the option to decide whether or not to complete the walking trial based on metronome pace.…”

Effort-Based Decision-Making and Gross Motor Performance: Are They Linked?

“…First, planning (conceiving of a strategy prior to carrying out an action) rather than decision-making may have been the cognitive construct that governed our gross motor task. Some researchers characterize planning as a part of decision-making in the context of gross motor performance [ 1 , 9 , 34 , 35 , 36 ]. However, for gross motor performance, decision-making may align with deciding whether or not to perform a task (i.e., “taking action”) or selecting from multiple ways to perform a task [ 9 ], rather than monitoring the performance of the task (i.e., matching steps to a metronome beat) [ 24 ].…”

“…However, for gross motor performance, decision-making may align with deciding whether or not to perform a task (i.e., “taking action”) or selecting from multiple ways to perform a task [ 9 ], rather than monitoring the performance of the task (i.e., matching steps to a metronome beat) [ 24 ]. Planning and decision-making may also have occurred serially rather than simultaneously [ 19 , 35 , 37 ] in our task: participants may have planned when to make initial heel contact prior to beginning the actual movement [ 14 , 15 , 16 , 17 ]. Thus, the neurological substrates involved in deciding on versus monitoring gross motor performance may be different [ 18 , 38 , 39 , 40 ].…”