Opinion
Full-body illusions and minimal phenomenal selfhood

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We highlight the latest research on body perception and self-consciousness, but argue that despite these achievements, central aspects have remained unexplored, namely, global aspects of bodily self-consciousness. Researchers investigated central representations of body parts and actions involving these, but neglected the global and unitary character of self-consciousness, the ‘I’ of experience and behaviour. We ask, what are the minimally sufficient conditions for the appearance of a phenomenal self, that is, the fundamental conscious experience of being someone? What are necessary conditions for self-consciousness in any type of system? We offer conceptual clarifications, discuss recent empirical evidence from neurology and cognitive science and argue that these findings offer a new entry point for the systematic study of global and more fundamental aspects of self-consciousness.

Introduction

Recent years have seen a flood of research into self-consciousness, and a renewed interest in its bodily foundations 1, 2. In philosophy of mind, there is widespread agreement that the core of the problem consists of understanding the pre-reflective bodily foundations of phenomenal selfhood (defined here as all those levels which are independent of explicit cognition and linguistic abilities, and which give rise to the subjective experience of being a self), but which can function as enabling conditions for a conceptually mediated, cognitive first-person perspective and high-level social cognition 3, 4, 5, 6, 7, 8. Prominent candidates are associated with notions such as ‘agency’ 9, 10, 11 and ‘embodiment’ (see Glossary). Here, we argue that from a strategic point of view, future research should focus on what we call ‘minimal phenomenal selfhood’ (MPS), which is related to the concept of embodiment and the simplest form of self-consciousness.

To illustrate this, we review how researchers have investigated embodiment and the bodily foundations of self-consciousness through the sense of ownership and identification with the body as a whole (phenomenally experienced ‘mineness’), self-location (centeredness of the conscious model of reality) and the first-person perspective. Next, we introduce a conceptual distinction between the conscious experience of ‘ownership for body parts’ (as studied in the rubber-hand illusion (RHI) [12]) and the experience of ‘global ownership’ (as studied in the full-body illusion [13]). We argue that only the latter enables investigations of MPS, with MPS being a clearer concept to guide future research. From a theory-of-science point of view, and given a complex domain such as human self-consciousness, we propose that an optimal strategy is likely to be the (initial) isolation of the simplest form of the target phenomenon. MPS is a phenomenal property, namely the conscious experience of being a self. It is the experience of being a distinct, holistic entity capable of global self-control and attention, possessing a body and a location in space and time.

Section snippets

MPS: conceptual foundations

MPS can be analyzed on phenomenological, representational and functional levels of description. Central defining features are, (i) a globalized form of identification with the body as a whole (as opposed to ownership for body parts), (ii) spatiotemporal self-location and (iii) a first-person perspective (1PP). It is important to differentiate between a weak and at least two stronger readings of ‘first-person perspective’, with MPS being partly constituted by the weak 1PP, and a necessary (but

Partial versus global ownership

Ownership for a body part can break down after damage to right temporo-parietal cortex, this is known as somatoparaphrenia 29, 30, 31. Somatoparaphrenic patients most often misattribute their contralesional hand as belonging to another person, mostly a familiar person (e.g. a doctor, nurse or friend) [31]. Other somatoparaphrenic patients suffer form the opposite pattern and self-attribute other people's hands when these are presented in their contralesional hemispace [29]. Somatoparaphrenia

Abnormal MPS in neurology

MPS breaks down in neurological patients with illusory global own body perceptions, called autoscopic phenomena 23, 27, 37, 47, 48, 49, that are characterized by seeing a second own body in extracorporeal space: autoscopic hallucination, heautoscopy, and out-of-body experience (Figure 1) (Box 2). Autoscopic phenomena are associated with multisensory disintegration and can be caused by focal brain damage (Figure 2) 26, 27. Recent neuroanatomical analysis indicated that autoscopic hallucinations

Further observations on MPS dimensions in autoscopic phenomena

In the majority of such autoscopic phenomena, MPS is characterized by a single visual weak 1PP, spatially overlapping self-location and non-ambiguous self-identification. Although under normal conditions humans experience a single visual weak 1PP, autoscopic phenomena indicate that conscious experience can also be characterized by the absence of a unitary visual weak 1PP, or by two simultaneous or rapidly alternating visual weak 1PPs. This is the case in patients with heautoscopy who claim to

Experimenting with MPS

Recent studies have extended clinical data on illusory global own body perceptions and studied MPS experimentally, refining the seminal self-observations made at the end of the 19th century by G.M. Stratton (Figure 3a) [54]. By exposing participants to conflicting multisensory bodily cues by means of mirrors, video technology or simple virtual reality devices 13, 28, 55, 56, these authors experimentally manipulated MPS. In particular, the presentation of stimuli in virtual reality set-ups has

Acknowledgements

T.M. is supported by a Fellowship at the Wissenschaftskolleg zu Berlin 2008/2009 and the Cogito Foundation. O.B. is supported by the Sandoz Family Foundation, the Cogito Foundation and the Swiss National Science Foundation.

Glossary

Agency
global motor control, including the subjective experience of action, control, intention, motor selection and the conscious experience of will. It involves the representation of goal-states.
Cognitive 1PP
arguably, this appears when a system possesses a concept of the strong 1PP and is able to apply this concept to itself (i.e. it has an abstract and active mental representation of itself as a subject of experience, which includes a special form of cognitive self-reference) [3,6–8]. The

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