Vestibular-somatosensory interactions affect the perceived timing of tactile stimuli.

Passive rotation has been shown to alter temporal-order judgments for tactile stimuli delivered to the hands giving an advantage to the leading hand. Here we measure thresholds for detecting stimulus onset asynchrony for touches on the hands during tilt to the left or right and during galvanic vestibular stimulation (GVS) that evoked illusory tilt. During tilt to one side, the effect of gravity on the otoliths is equivalent to a physical acceleration away from that side (e.g., tilt left is equivalent to accelerating rightwards). We therefore predicted a "leading hand advantage" for the hand opposite to the tilt direction. Thresholds for detecting asynchronicity for left-hand-first and right-hand-first touches (defined as correct detection 75% of the time) were measured separately using interleaved adaptive staircases for 15 participants. For both physical and illusory tilt there was a temporal advantage for stimuli presented to the hand contralateral to the tilt-equivalent to the "leading hand" during passive rotation. That is, there was a temporal advantage for the upward hand (for physical tilt) and for the anodal-side hand (for illusory tilt caused by GVS). These results are discussed in terms of attention and direct sensory components evoking the "leading hand" bias. These findings add to the emerging understanding of the pervasive role of vestibular activity in many aspects of cognitive processing.