Vestibular discrimination of gravity and translational acceleration.

According to Einstein's equivalence principle, linear accelerations experienced during translational motion are physically indistinguishable from changes in orientation relative to gravity experienced during tilting movements. Nevertheless, despite these ambiguous sensory cues provided by the primary otolith afferents, perceptual and motor responses discriminate between gravity and translational acceleration. There is growing evidence to suggest that the brain resolves this ambiguity primarily by combining signals from multiple sensors, the semicircular canals being a main extra otolith contributor. Here, we summarize the experimental evidence in support of the canal influences on the neural processing of otolith cues, provide specific experimental results in rhesus monkeys, and discuss and compare previously proposed models that combine otolith and semicircular-canal signals in order to provide neural estimates of gravity and linear acceleration.