Assessing Multisensory Integration In Reaching Space

Claudio Brozzoli, INSERM U864 "Espace et Action"

Abstract
Does voluntary action affect the visuo-tactile (VT) coding of peripersonal space (PS)? To answer this question, healthy subjects discriminated tactile stimulation on their right hand (up-index/down-thumb) while grasping a differently oriented object (embedded with visual distractors) with the stimulated right hand or, as a control, the left hand.
Before movement initiation the VT interference (VTI) was larger when the object’s main axis was spatially compatible with the axis formed by index and thumb. Crucially, right-hand action modulated the VTI that increased at the onset of the grasping movement and during its execution. This on-line multisensory effect was selective for object orientations that were incompatible with the right-hand posture before movement start. No difference was observed for compatible orientations across the reach-to-grasp phases. In the control condition the three action phases and object orientations did not modulate the VTI.
The results support the hypothesis that performing an action can affect the multisensory coding of the PS. These findings constitute the first experimental evidence that action-dependent modulations are selective for the body-part involved in the action. They suggest that multisensory integration involving an object in action space can dynamically vary according to the different phases of an ongoing action towards it.

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