Visual-Oculomotor and Head Movement Strategies in Postural Control
Postural control requires the integration of visual, vestibular, and proprioceptive information to maintain stability. The gold standard for inferring postural control relies on lab-based tools, such as force plates and full-body motion capture to track center of mass (COM) and center of pressure (COP). However, these tools are impractical for assessing balance in real-world or applied settings. Evolving, portable technology provides the opportunity to track head and eye movements, which reflect both biomechanical adjustments and sensory integration, and may serve as an alternative for evaluating postural stability. This dissertation investigates the use of head and eye movements as markers of postural control and balance strategies. In the first study, the relationship between head position and COM was compared during quiet stance to determine if movement of the head could serve as a direct proxy for COM. Investigation of this relationship was grounded in the premise that if the inverted pendulum model of COM were to be extended to include the head, then movement patterns between head position and COM would be tightly coupled. Results from this study reflected strong linear relationships between head position and COM, with the highest synchronization in the mediolateral direction. These results align with the inverted pendulum model demonstrating that COM is based on a variety of joints. While the relationship between head position and COM was synchronized, head position did show more variability than traditionally measured COM. This was due to the added degrees of freedom induced from the additional body segments added when the inverted pendulum model was extended to include the head. This study supports the use of head metrics as an accessible indicator of static postural control. The second study explored head and eye movement strategies using a head-mounted eye and motion tracking system during a dynamic, tandem gait walking task utilizing expert and novice balancers. Results were interpreted as exploratory data due to insufficient statistical power, however, several data trends aligned with expectations deduced from previous literature. Expert balancers consistently displayed head and eye movement behaviors that optimized the function of the vestibular and visual sensory systems, effectively reducing the number of performance errors and displaying greater postural control in comparison to that of novice balancers. These two studies provide evidence that head and eye metrics may serve as practical tools for assessing postural control and as behavioral indicators for evaluating optimal balance strategies. These studies offered novel insight into the mechanisms of postural stability with potential implications for the assessment and interventions in athletic, clinical, and aging populations.
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