The representation of peripersonal space around upper and lower limbs

Peripersonal space (PPS), the space closely surrounding the body, is typically characterised by enhanced multisensory integration. Neurophysiological and behavioural studies have consistently shown stronger visuo-tactile integration when a visual stimulus is presented close to the tactually stimulate body part in near space (within PPS) than in far space. However, in the majority of these studies tactile stimuli were delivered to the upper limbs, torso and face. Therefore, it is not known whether the space surrounding the lower limbs is characterised by similar multisensory properties. To address this question we asked participants to perform two versions of the classic visuo-tactile crossmodal congruency task in which they had to perform speeded elevation judgements of tactile stimuli presented to the dorsum of the hand and foot while a simultaneous visual distractor was presented at spatially congruent or incongruent locations either in near or far space. In line with existing evidence, when the tactile target was presented to the hand the size of the crossmodal congruency effect (CCE) decreased in far as compared to near space suggesting stronger visuo-tactile multisensory integration within PPS. By contrast, when the tactile target was presented to the foot, the CCE was weaker for visual distractor in near than far space. A follow-up study confirmed that these results were not driven by the effector used to execute the response. These findings show systematic differences between the representation of PPS around upper and lower limbs, suggesting that the multisensory properties of the different body-part centred representations of PPS are likely to depend on the potential actions performed by the different body parts.