  Background: Stochastic resonance (SR) refers to a faint signal being enhanced
with the addition of white noise. Previous studies have found that vestibular
perceptual thresholds are lowered with noisy galvanic vestibular stimulation
(i.e., "in-channel" SR). Auditory white noise has been shown to improve tactile
and visual thresholds, suggesting "cross-modal" SR. Objective: We aimed to
study the cross-modal impact of noisy galvanic vestibular stimulation (nGVS)
(n=9 subjects) on visual and auditory thresholds. Methods: We measured auditory
and visual perceptual thresholds of human subjects across a swath of different
nGVS levels in order to determine if a subject-specific best nGVS level
elicited a reduction in thresholds as compared the no noise condition (sham).
Results: We found an 18% improvement in visual thresholds (p = 0.026). Among
the 7 of 9 subjects with reduced thresholds, the average improvement was 26%.
Subjects with higher (worse) visual thresholds with no stimulation (sham)
improved more than those with lower thresholds (p = 0.005). Auditory thresholds
were unchanged by vestibular stimulation. Conclusions: These results are the
first demonstration of cross-modal improvement with nGVS, indicating galvanic
vestibular white noise can produce cross-modal improvements in some sensory
channels, but not all.
