Abstract
Abstract
Standing balance relies on the continuous detection of body motion across a wide range of amplitudes and frequencies. According to Weber’s law, sensory discrimination should degrade in proportion to stimulus amplitude, yet vestibular self-motion perception deviates from this prediction. Whether this deviation extends to the vestibular control of posture remains unknown. To test this hypothesis, we delivered amplitude-increasing electrical vestibular stimulation (EVS, 0-2 mA) at four frequencies (0.1, 0.2, 0.5, and 1 Hz) to 10 healthy young adults, and quantified balance discrimination thresholds (DTs) from the gain and inter-trial variability of the lateral ground reaction force, using signal detection theory. Balance control DTs increased sublinearly with EVS amplitude at all frequencies, deviating from Weber’s law. Both balance-correcting response gain and variability accounted for this deviation: gain decreased more slowly than the strictly inverse relationship that would have alone produced strict adherence to Weber’s law, while variability exhibited an initial increase followed by saturation at higher EVS amplitudes, a signal-dependent structure necessary to reproduce the observed DT pattern. EVS frequency modulated the shape of this deviation but affected neither overall DT nor the signal-to-noise ratio of the balance-correcting response, which instead remained similar across frequencies. This study revealed a particular property of postural control discrimination by extending the psychophysical and neural deviations from Weber’s law previously reported for vestibular perception. Overall, these results provide a better understanding of the balance control discrimination process and provide potential additional assessment criteria for vestibular impairments.
Significance Statement
Maintaining upright balance requires detecting body motion across a wide range of sway dynamics. Whether this capacity holds when a vestibular stimulus is stronger remains unclear. Using electrical vestibular stimulation of increasing amplitude, we report that the postural control system’s ability to detect changes in vestibular input does not decline as abruptly as classically predicted with increasing stimulus strength. Both the gain and the variability of the balance-correcting responses shaped this precision. These results improve our understanding of the postural control system’s ability to maintain balance in response to a wide range of vestibular stimuli and offer a tool for quantifying accuracy of the balance control system in both fundamental and clinical research.