Automatic Facilitation ofMovements by Tactile Input: Evidence for a Somatomotor Route in Spatial Orienting

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lt is well-established that salient stimuli (exogenous cues) facilitate perception. Here, we addressed whether salient stimuli also facilitate action, and through what route this is mediated. Participants responded to a non­spatial imperative response signa! with button press using their left or right thumb. At different intervals prior to the response signa! a left or right tactile, auditory or visual stimulus was presented, whose side was independent from the required response side. To distinguish between influences that do and do not rely on spatial representations participants either held their hands in front of their body midline or to the left or right of it. We observe that only tactile stimuli facilitated movement at the side of the task-irrelevant stimulus, and that this occurred independent of the hand position in extemal space. Whereas previous studies have attributed the influence of salient stimuli on perception to supramodal spatial representations as contained in the fronto-parietal ventral attentional network, our data suggest a complementary, more direct, route through which salient tactile events may trigger orienting responses in action, which relies on direct connections between somatosensory and motor areas of the brain.
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