Keeping in Touch with One's Self: Multisensory Mechanisms of Self-Consciousness

Abstract

BackgroundThe spatial unity between self and body can be disrupted by employing conflicting visual-somatosensory bodily input, thereby bringing neurological observations on bodily self-consciousness under scientific scrutiny. Here we designed a novel paradigm linking the study of bodily self-consciousness to the spatial representation of visuo-tactile stimuli by measuring crossmodal congruency effects (CCEs) for the full body.Methodology/Principal FindingsWe measured full body CCEs by attaching four vibrator-light pairs to the trunks (backs) of subjects who viewed their bodies from behind via a camera and a head mounted display (HMD). Subjects made speeded elevation (up/down) judgments of the tactile stimuli while ignoring light stimuli. To modulate self-identification for the seen body subjects were stroked on their backs with a stick and the felt stroking was either synchronous or asynchronous with the stroking that could be seen via the HMD.We found that (1) tactile stimuli were mislocalized towards the seen body (2) CCEs were modulated systematically during visual-somatosensory conflict when subjects viewed their body but not when they viewed a body-sized object, i.e. CCEs were larger during synchronous than during asynchronous stroking of the body and (3) these changes in the mapping of tactile stimuli were induced in the same experimental condition in which predictable changes in bodily self-consciousness occurred.Conclusions/SignificanceThese data reveal that systematic alterations in the mapping of tactile stimuli occur in a full body illusion and thus establish CCE magnitude as an online performance proxy for subjective changes in global bodily self-consciousness.

Force feedback facilitates multisensory integration during robotic tool use

“…The delay in FFB resulted in an unrealistic FFB and as a consequence may have decreased the integration of the tool in the body representation, as reflected by a smaller CCE. This result is reminiscent of the findings by Pavani et al (2000), who showed that the CCEs were smaller when rubber hands were placed in an anatomically impossible position, suggesting that the CCE provides a measure of hand ownership and body ownership (see also Aspell et al 2009). …”

“…All numerical values represent the mean and between-subject standard error. The results focused primarily on the RTs rather than errors, since it has been shown that RTs are more sensitive for the CCE (Pavani et al 2000;Aspell et al 2009;Shore et al 2006;Sengül et al 2012).…”

“…The CCE is defined as the performance difference (reaction time or accuracy) between incongruent and congruent visuo-tactile stimulations and is typically larger when the visual and tactile stimuli are closer to each other in space ). Visuo-tactile CCEs have been proposed to reflect the perceived proximity between visual and tactile stimuli and thereby provide an objective measure of the ease whereby multimodal information is integrated in the body representation (Zopf et al 2010;Pavani et al 2000;Aspell et al 2009). Using the CCE, it has been found that active tool use increases the interference of visual stimuli presented at the tip of tools with vibrotactile stimuli presented on the hand that holds the tool (Maravita et al 2002).…”

Bodily self: an implicit knowledge of what is explicitly unknown

“…Based on their functional neuroimaging (fMRI) data, Myers and Sowden proposed that the right EBA may perform an important sorting of body-part images by identity (including self-recognition). More direct evidence for the hypothesis that in the self-related processes, we combine visual, somatosensory, proprioceptive, and motor information comes from the literature based on behavioral and imaging studies on the rubber hand illusion (RHI) and the full body ownership illusions (Ehrsson et al 2005;Tsakiris and Fotopoulou 2008;Makin et al 2008;Aspell et al 2009;Slater et al 2009). There seems to be consensus in this literature that the processing of one's own body relies on multisensory integration mechanisms.…”

Illusory self-identification with an avatar reduces arousal responses to painful stimuli

“…In the rubber hand illusion (RHI), the visuo-tactile congruent stimulation of one's own hidden hand and a visible anatomical compatible fake hand induces the sensation that the prosthetic limb belongs to oneself [4,11]. Similarly, the full body illusion (FBI) can be induced; thus, congruent visuo-tactile stimulation at the trunk can induce self-identification and self-location changes with respect to a virtual or fake body [12,13,9,14].…”