Abstract
Self-touch is considered important for bodily self-consciousness and self-other distinction and has been reported to improve clinical symptoms of disembodiment. To investigate the link between self-touch and disembodiment in healthy participants, we studied the effect of self-touch versus touch produced by another person (other-touch) on experimentally induced disembodiment. In a mixed reality paradigm, across two experiments, participants could see their own body and surroundings with a controllable visual delay and either stroked their own hand with a paintbrush or were stroked with it by the experimenter. Experiment 1 first assessed the sensitivity to temporal multimodal mismatches and delay-induced changes in the sense of body ownership in three conditions, namely self-touch, other-touch and hidden-self-touch (visually occluding the touching hand). In a second block, we compared phenomenological and physiological (threat response) measures of disembodiment between the self-touch and other-touch conditions. Experiment 2 roughly replicated the first block of Experiment 1 but included a condition in which participants performed the self-touch gesture without touching their hand. Such experiment attempted to control for the potential role of efferent signals. Our results show that increasing visual delay generally enhances the feeling of disembodiment, yet the decrease of body ownership is less pronounced during self-touch. For sensitivity to delay between conditions, however, diverging findings are discussed. This study provides evidence for the importance of self-touch in sustaining a healthy sense of body in the context of disembodiment.
Highlights
Self-touch is considered important for the development (Rochat & Hespos, 1997) and maintenance of bodily self-consciousness and selfother distinction (Boehme, Hauser, Gerling, Heilig, & Olausson, 2019; Hara et al, 2015; Husserl, 1952; Slatman, 2009)
Our results show that increasing visual delay generally enhances the feeling of disembodiment, yet the decrease of body ownership is less pronounced during self-touch
The point of subjective equality (PSE) was higher in the other-touch condition (M = 443 ms, SD = 107 ms) than in both the self-touch (M = 388 ms, SD = 134 ms) and the self-no-touch condition (M = 373 ms, SD = 107 ms)
Summary
Self-touch is considered important for the development (Rochat & Hespos, 1997) and maintenance of bodily self-consciousness and selfother distinction (Boehme, Hauser, Gerling, Heilig, & Olausson, 2019; Hara et al, 2015; Husserl, 1952; Slatman, 2009). During self-touch the corresponding tactile perception is attenuated in both the intensity of the sensation (Bays, Flanagan, & Wolpert, 2006; Blakemore, Frith, & Wolpert, 1999) and the related brain activation (Blakemore, Wolpert, & Frith, 1998; Boehme et al, 2019; Kilteni & Ehrsson, 2020). To account for this, a ‘forward model’ has been proposed, suggesting that the attenuation of tactile signals results from predicting the consequences of self-generated movement (Bays et al, 2006; Blakemore et al, 1999; Kilteni, Engeler, & Ehrsson, 2020), potentially explaining the incapacity to tickle ourselves (Blakemore, Wolpert, & Frith, 2000; Weiskrantz, Elliott, & Darlington, 1971). Patients with disturbances of self-consciousness such as in schizophrenia, showed altered self-monitoring mechanisms (Blakemore, Smith, Steel, Johnstone, & Frith, 2000; Frith, 1987; Synofzik, Thier, Leube, Schlotterbeck, & Lindner, 2010; Voss et al, 2010), and in patients with hallucinations reduced sensory attenuation as response to self-touch has been reported (Blakemore, Wolpert, & Frith, 2000)
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