Walking on a line: A motor paradigm using rotation and reflection symmetry to study mental body transformations Bérangère Thirioux a,b, * , Gérard Jorland b , Michel Bret c , Marie-Hélène Tramus c , Alain Berthoz a a Laboratoire de Physiologie de la Perception et de l’Action, Collège de France, France b Ecole des Hautes Etudes en Sciences Sociales, Paris, France c Arts et Technologies de l’Image, Université Paris 8, Saint-Denis, France article info Article history: Accepted 2 February 2009 Available online 18 March 2009 Keywords: Reflection–rotation symmetry Embodiment Self-location Mental body transformation Spontaneous perspective-taking abstract Researchers have recently reintroduced the own-body in the center of the social interaction theory. From the discovery of the mirror neurons in the ventral premotor cortex of the monkey’s brain, a human embodied model of interindividual relationship based on simulation processes has been advanced, according to which we tend to embody spontaneously the other individuals’ behavior when interacting. Although the neurocognitive mechanisms of the embodiment process have started being described, the mechanisms of self-location during embodiment are still less known. Here, we designed a motor para- digm which allows investigating in ecologically more valid conditions whether we embody another per- son’s intransitive action with an embodied or disembodied self-location. Accordingly, we propose a phenomenological model of self–other interaction showing how perspective-taking mechanisms may relate on mental body transformation and offering a promising way to investigate the different sorts of intersubjectivity. Ó 2009 Elsevier Inc. All rights reserved. 1. Introduction Since the last decade, cognitive neuroscientists (Blanke & Metz- inger, 2009; Gallagher, 2000, 2005; Metzinger, 2003, 2008; Ruby & Decety, 2001) have restored the own-body in the center of the the- ory of the self, revealing its importance for the development of a comprehensive selfhood theory. While providing us with the feel- ing of being positioned at a specific location in space, the own-body is immediately experienced as the spatial location of the self (Arzy, Thut, Mohr, Michel, & Blanke, 2006; Blanke et al., 2005), leading to the coherent and normal experience of the spatial unity between the self and the body – or ‘‘embodied self-location” (Blanke & Metz- inger, 2009). In the same time, the own-body has also been reintro- duced in the theory of social interactions, as phenomenologists at the beginning of the 20th had already assumed (Lipps, 1897, 1903, 1906, 1913; Vischer, 1927; Husserl, Hua XIII-XVI). First, the mechanisms of self-location have been hypothesized to be involved in the mechanisms of self–other distinction (Decety & Sommerville, 2003; Ruby & Decety, 2001, 2004). Indeed, the own-body as origi- nate center of orientation mediates our own egocentered visuo- spatial perspective (Zahavi, 1994) that we can experience only in a direct way (Husserl, Hua XIII-XVI; Berthoz, 2004; Vogeley & Fink, 2003; Zahavi, 1994) whereas taking the other’s visuo-spatial per- spective has been hypothesized to rely on a mental translocation of the egocentric viewpoint (Vogeley & Fink, 2003), i.e., on a rather indirect process (Berthoz, 2004; Jorland, 2004; Jorland & Thirioux, 2008). Second, inspired by the discovery of the mirror neurons in the ventral premotor cortex of the monkey’s brain (di Pellegrino, Fadiga, Fogassi, Gallese, & Rizzolatti, 1992; Rizzolatti, Fogassi, & Gallese, 2001), current theories of social interactions have proposed a human embodied model of interindividual relationship based on simulation processes (Carr, Iacoboni, Dubeau, Mazziotta, & Lenzi, 2003; Fadiga, Craighero, & Olivier, 2005; Gallese, 2007; Rizzolatti, Fadiga, Fogassi, & Gallese, 1999). Accordingly, understanding an- other individual’s actions (Buccino et al., 2001), emotions (Carr et al., 2003) or intentions (Iacoboni et al., 2005) may require the observation of his (her) behavior in a specific context and then addi- tional cognitive elements (Gallagher, 2008) such as the activation of internal models by which we simulate the other’s behavior (see also Zahavi, 2008; for the rehabilitation of the direct perception in social cognition, see Gallagher, 2008). For instance, it has been shown that individuals change their breathing when observing other individu- als performing effortful actions (Blakemore & Frith, 2005; Paccalin & Jeannerod, 2000) and a recent fMRI study on sense of touch re- vealed that touch observation activates the secondary somatosen- sory cortex, suggesting visuo-tactile mirroring mechanisms in this brain area (Ebisch et al., 2008). In the aggregate, the own-body may thus be involved in several phenomenological aspects of the self, such as self-location, self–other distinction, and self–other 0278-2626/$ - see front matter Ó 2009 Elsevier Inc. All rights reserved. doi:10.1016/j.bandc.2009.02.006 * Corresponding author. Address: Laboratoire de Physiologie de la Perception et de l’Action, Collège de France, 11, place Marcelin Berthelot, 75231 Paris Cedex 05, France. Fax: +33 (0) 1 44 27 13 82. E-mail address: berangere.thirioux@college-de-france.fr (B. Thirioux). Brain and Cognition 70 (2009) 191–200 Contents lists available at ScienceDirect Brain and Cognition journal homepage: www.elsevier.com/locate/b&c