Visuo-tactile integration in personal space

Integration of information across sensory modalities is enhanced when stimuli in both modalities are in the same location. This ‘spatial rule’ of multisensory integration has been primarily studied in humans by comparing stimuli located either in the same vs. opposite side of the body midline or in peripersonal vs. extrapersonal space, both of which involve large, categorical differences in spatial location. Here we used psychophysics and event-related potentials (ERPs) to investigate visuo-tactile integration in personal space (i.e., on the skin surface). We used the mirror-box technique to manipulate the congruence of visual and tactile information about which finger on either the right or left hand had been touched. We observed clear compatibility effects for both visual and tactile judgments of which finger on the left hand had been touched. No such effects, however, were found for judgments about the right hand. ERP data showed a similar pattern. Amplitude of the vertex P200 potential was enhanced, and that of the N2 reduced, for congruent visuo-tactile events on the left – but not the right – hand. Similarly, a later positivity over posterior parietal cortices (P300) showed bilateral enhancement for congruent visuo-tactile events on the left hand, but only contralateral enhancement for events on the right hand. These results provide clear evidence for spatial constraints on visuo-tactile integration defined in personal space, and also reveal clear lateralisation of these effects. Further, these results link these ‘ultra-precise’ spatial constraints to processing in the right posterior parietal cortex