Title: Investigating the Modulation of Motor Effort Costs by Posture in Visual Exploration
Supervisors: Dr. Nicola Hodges; Dr. Alan Kingstone
Committee member: Dr. Romeo Chua
Abstract: Visual exploration is an active, embodied process relying on the coordinated movements of the eyes, head, and body. Prior research demonstrated that posture (sitting, standing, swiveling) significantly alters this multi-effector coordination during exploration in virtual reality (VR). However, the underlying mechanism driving these postural differences remains unclear. This thesis investigates whether these coordination changes stem from variations in the motor effort required to orient the visual system in different postures. To probe the influence of motor effort, I leverage the established motor-memory trade-off framework, which posits that individuals balance cognitive costs (e.g., using working memory) against physical costs (e.g., executing movements) to optimize behavior. Specifically, increased motor effort typically leads individuals to rely more on internal cognitive resources rather than engaging in effortful external information sampling. Applying this framework, I hypothesize that postures imposing constraints on mobility for visual orienting will consequently induce greater reliance on working memory, due to the increased motor effort costs of re-orienting gaze. To test this, participants performed a block-copying task (Ballard et al., 1995) as their gaze and body movements were recorded. Specifically, participants will be instructed to reproduce patterns from a model screen presented at varying angles (45°, 90°, 135°, 180°) while assuming each of three postures (Sit, Swivel, Stand). Visual sampling behavior (e.g., number of gaze shifts between model and workspace, dwell time on model) and effector kinematics will be measured. I predict that conditions thought to require greater motor effort (e.g., stationary sitting, larger angles) will lead to behavior indicative of increased memory reliance (e.g., fewer gaze shifts to the model, longer dwell times per look). Furthermore, I predict an interaction, with postural differences in sampling strategy being most pronounced at larger angles where mobility constraints are most impactful. Findings are expected to provide direct evidence linking biomechanical constraints (via posture) and associated motor effort to cognitive trade-offs during information acquisition. This work offers a mechanistic account for posture effects on visual exploration in line with an embodied view of human cognition.