Multisensory integration in body perception is unaffected by concurrent interoceptive and exteroceptive tasks

A recent study (Tsakiris et al., 2011) suggested that lower interoceptive sensitivity, as assessed by heat-rate estimation, predicts malleability of body representations, as measured by proprioceptive drift and ownership in a rubber hand illusion (RHI) task. The authors suggested that one explanation of their finding is linked to the notion of limited attentional resources: individuals with high interoceptive sensitivity are more aware of internal states and, in turns, they have less attentional resources available for multisensory processing. If this is the case, the competition between interoceptive and multisensory processing should be strongest when they are concurrent. Here we tested this prediction using a visuo-proprioceptive conflict produced through prismatic goggles, without affecting body ownership (unlike the RHI). In three experiments, participants looked at their own hand while wearing neutral or prismatic goggles (visual field shifted 20° leftwards). Meanwhile, they performed a concurrent counting tasks on interoceptive (Exp. 1–2: heart-beats; Exp. 3: breaths) or exteroceptive signals (pure-tones). A no-task condition was also included. We measured proprioceptive drift in each condition an indicator of illusion strength. All experiments documented a significant drift of perceived hand position after prism exposure. This bodily illusion, however, was never affected by the concurrent task, regardless of whether it involved interoceptive or exteroceptive signals. These result reveal that multisensory integration underlying body perception is unaffected by concurrent tasks capturing attentional resources, strongly suggesting a low-level and automatic phenomenon. Furthermore, they indicate that the origin of increased body malleability in individuals with low interoceptive awareness is not competition for attentional resources.