Sensory interactions for human balance control revealed by galvanic vestibular stimulation

Many types of sensory information are known to contribute to the human balance control process but little is known about how the different sensory channels interact. Here we consider the postural response to a perturbation delivered to the vestibular channel using galvanic vestibular stimulation. We show that the response is modified by the absence of information in the other sensory channels. Removal of somatosensory information leads to a massive increase in response size. Similarly, removal of visual information augments the response. Furthermore, the response size is graded according to the amount of visual information available. These effects occur through two processes. One that influences the developing response through feedback mechanisms and another that influences the initial response selection through gain changes. The latter is described as a competitive process that can be likened to a proportional representation voting system.