Abstract
Postural control is often portrayed as largely reflexive and automatic, yet a broad body of work shows that upright stance also recruits higher-level, decision-like processes. These cognitive influences emerge alongside multisensory contributions from vestibular, somatosensory/proprioceptive, and visual systems, and they help explain age- and context-dependent instability and falls. To isolate higher-level control from peripheral biomechanics and reflexes, we employ a visually simulated inverted pendulum (VIP) balancing task. Because VIP task does not load the controller (joystick or forceplates), it elicits minimal reflexive upper-limb responses and instead spotlights discrete, decision-like command selection (among inaction, corrective, anticipation, and destabilization), a structure also observed in related self-balancing paradigms. Study 1 used VIP to examine how aging alters these command dynamics. We partitioned balancing into Safe (moving toward upright), Saved (approaching a boundary but recovered), and Failed (approaching and crashing into a boundary) regimes and showed that age differences concentrate where time pressure is greatest: near imminent falls. Older adults generated fewer corrective and more destabilizing commands than younger adults, specifically in Failed balancing; Logistic functions best captured how command probabilities evolve as a function of time left to fall, with younger adults switching earlier toward fall-saving corrections.
Study 2 asked whether training these decision-like command strategies in the VIP can be improved and generalized to real bipedal stance across modalities. We trained participants on the VIP using a joystick or forceplates (unimanual and bimanual) configuration, then assessed beam-stance performances pre/post of the VIP training. Building on Study 1’s regime framework, we also quantified strategy use during training and how this coupling changed with practice. VIP training reduced narrow-beam fall rates and were also partially effective on reducing sway in wide-beam, relative to baseline (no corresponding improvement in the hand-eye coordination trained control group). Training altered the mapping between momentary fall frequency and corrective choice.
Together, the studies advance a regime-specific, time-critical view of balance control: when imminent falls compress decision time, successful stabilization hinges on prompt switching to corrective commands. The VIP therefore complements stance assays by making higher-order control observable and trainable, while providing principled hypotheses about how such learned policies may map onto lower-limb control during real-world posture.