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Session: Motion
Session starts: Thursday 26 January, 14:30
Presentation starts: 15:00
Room: Room 531

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Romain Tisserand (University of Poitiers)
Brandon Rasman (Erasmus MC)
Nina Omerovic (Erasmus MC)
Ryan Peters (University of Calgary)
Jean-Sebastien Blouin (University of British Columbia)
Patrick Forbes (Erasmus MC)

Abstract:
The instability of human standing demands that the brain accurately perceive balancing self-motion and determines whether movements originate from self-generated actions or external disturbances. Here, we examined how humans perceive their motor actions while balancing upright by assessing their perception thresholds to external disturbances during active balance and passive (immobile) standing. We find that the conscious sense of balance can be distorted by the corrective control of upright standing. Healthy participants actively balanced or stood immobile on a robotic balance simulator while whole-body or ankle perturbations were injected into the loop of ongoing control. We used psychometric curves to estimate perception thresholds to the imposed perturbations and balance responses, which evoked cues of self-motion that were above and below the statistics of their naturally occurring corrective balance actions. When standing immobile, participants clearly perceived imposed perturbations. Conversely, when freely balancing, participants often misattributed their own corrective responses as imposed motion because their balance system had detected, integrated, and responded to the perturbation in the absence of conscious perception. Importantly, this only occurred for whole-body perturbations (but not ankle perturbations) that remained below the natural variability of ongoing balancing oscillations since they were encoded ambiguously with the balance-correcting responses. These findings reveal that our balance system operates on its own sensorimotor principles that can interfere with causal attribution of our actions, and that our conscious sense of balance depends critically on the source and statistics of induced and self-generated motion cues. They further hold clinical relevance for aging and populations with certain pathologies (e.g., vestibular and cerebellar patients), where the expected increase in sensory and motor noise could widen the natural variability of standing and cause misattributions of self-motion at perturbation magnitudes that may threaten stability.