Stochastic resonance in vestibular perceptual thresholds for translation but not rotation

Stochastic resonance, in which adding a certain amplitude of noise improves sensory information transfer, has been observed in vestibular perceptual thresholds, particularly for roll tilts. The semicircular canals and otolith organs are both stimulated during roll tilt, so it is yet to be determined whether vestibular perceptual stochastic resonance involves the canals or otoliths (or both). Animal studies have shown galvanic vestibular stimulation (GVS) stimulates both the canal and otolith afferent neurons. In one human study, noisy GVS (nGVS) at a single subject-specific amplitude improved thresholds for translations (stimulating the otolith organs), but not for rotations (primarily stimulating the canals). However, these studies did not investigate the exhibition of stochastic resonance with nGVS, which requires identifying a dip in thresholds with increasing amplitude of nGVS. We tested human thresholds for roll rotation about an Earth-vertical axis while the subject was supine (canals) and inter-aural translation in an Earth-horizontal axis while seated upright (otolith organs), each while applying a broad range of different nGVS amplitudes (0 to ± 700 µA peak-to-peak) to identify the presence of stochastic resonance (i.e., the theoretical shape of threshold improvement with an optimal amplitude of nGVS). Six of 11 subjects (55%) exhibited stochastic resonance for inter-aural translation by our most rigorous criterion (significantly higher proportion than expected with no underlying stochastic resonance based upon simulations, p = 0.001), in contrast to only 1 of 12 subjects (8.3%) for roll rotation ( p = 0.239). We conclude stochastic resonance in vestibular perceptual thresholds using nGVS is much more common for otolith-mediated motions (e.g., translation), as compared to canal-mediated rotations. Thus, nGVS can extend the operating range of the otolith-mediate perceptual system in some individuals.