Vestibular control of posture deviates from Weber's law in response to electrical vestibular stimulation

Sustaining balance depends on sensing one's body movements, spanning a broad spectrum of velocities and frequencies. Weber's law posits that sensory detection should decline in tandem with stimulus intensity, yet the vestibular system's perception of self-motion diverges from this expectation. The extent of this divergence in vestibular control of posture remains unclear.

To examine this, 10 healthy young adults were subjected to amplitude-increasing electrical vestibular stimulation (EVS, ranging from 0.0 to 2.0 mA) at four frequencies (0.1, 0.2, 0.5, and 1.0 Hz). By assessing balance discrimination thresholds (DTs) using the gain and inter-trial variability of lateral ground reaction force, signal detection theory was employed.

The DTs for balance control rose at a rate less than predicted by Weber's law, indicating a deviation from the law. This deviation was attributed to both the balance-correcting response gain and to the variability in the response. The gain exhibited a slower decrease than the inverse relationship necessary for strict adherence to Weber's law, while the variability initially increased and then plateaued at higher EVS intensities, a signal-dependent phenomenon that contributed to the observed DT pattern.

EVS frequency impacted the shape of this deviation but did not alter the overall DT or the signal-to-noise ratio of the balance-correcting response, which remained constant across frequencies. This research illustrates a distinct characteristic of postural control discrimination, expanding the concept of deviations from Weber's law observed in vestibular perception.

Collectively, these findings enhance comprehension of the balance control discrimination mechanism and can serve as supplementary diagnostic markers for vestibular disorders.