Uncovering dual pathways for the sense and control of balance through reaction-time analysis

Abstract

Reaction-time paradigms are widely used to investigate multisensory processing and sensorimotor integration, yet their application to postural control has been limited. This may stem from the view that most self-generated balance-correcting motor actions occur without conscious awareness. However, this contrasts with evidence that reaction times to external stimuli can still be modulated during balance tasks (e.g., sitting, standing, walking), suggesting that even automatic balance control can interact with higher-level cognitive processing. Yet the temporal dynamics distinguishing automatic postural from consciously mediated responses to balance perturbations remain underexplored. In this study, we used a robotic balance simulator to impose disruptions to ongoing balance and dissociate balance-correcting and perceptual mechanisms of standing balance control. Participants stood on a robotic simulator that applied 200 ms torque perturbations of varying amplitudes. Additional ankle torque perturbations mimicking natural balance-control statistics were delivered to artificially increase ongoing motor noise. We recorded both EMG-based corrective muscle responses and perceptual reaction times via button presses, enabling direct comparison of automatic and conscious responses. Both response types decreased with increasing perturbation amplitude, consistent with findings from other sensory domains. Crucially, perceptual reaction times increased with higher noise amplitudes, whereas automatic postural responses did not. This dissociation highlights distinct neural mechanisms underlying conscious perception and postural control based on the functional purposes these processes fulfill.