NOTE-1002: Blanke & Metzinger — Full-body illusions and minimal phenomenal selfhood

Contribution

The paper names a target for the science of bodily self-consciousness, minimal phenomenal selfhood (MPS), and breaks it into three dimensions that can be measured or reported separately: self-identification with the body as a whole, self-location, and a weak first-person perspective. It then sorts the existing evidence by whether it touches those dimensions. The rubber-hand illusion and somatoparaphrenia, the field’s main tools for ownership, are put on the side of partial ownership and said not to reach MPS. Out-of-body experience, heautoscopy and the new full-body illusions are put on the side of global ownership. From that sorting it draws a thesis: agency is a causal background to selfhood, not part of it.

Key insight

The simplest self is a whole-body thing: being identified with one body, located where it is, and seeing from inside it. Owning a hand is not a small piece of that; it can be disturbed while the self stays whole, and the self can be displaced while every part is still one’s own. On this view a body-part illusion and an out-of-body experience are different kinds of evidence, and only the second reaches selfhood.

Assumptions

• The self-model theory. Concepts and the strong 1PP come from Metzinger’s Being No One (LIT-467) and its précis. MPS is “the representational content” of an integrated state that “for the first time makes the body available for attention and global control”, and it is felt as a self because the body model “is phenomenally transparent because it cannot introspectively be recognized as a model” (p. 8).
• Strategy: isolate the simplest form first. “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” (p. 7). The rest of the paper depends on MPS being that form.
• Reports and drift measure the dimensions. In the full-body illusion, “Questionnaire scores were used to quantify self-identification and perceived body position (drift) to quantify self-location” (p. 12). The patients’ dimensions are read from their descriptions (Box 2).
• “Necessary” in the metaphysical sense. The agency thesis is about “the minimal supervenience base for phenomenal selfhood” (p. 12), and the Box 1 definitions separate what is necessary from what is only “causally enabling” (p. 8). Evidence from adult humans is taken to bear on that base.

Key results

The paper has no data of its own. Its moves, in order:

• Definition (p. 7). “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.”
• Three readings of “first-person perspective” (p. 8, glossary). The weak 1PP is “a purely geometrical feature of an egocentric model of reality”, a centre of projection. The strong 1PP appears when the system “is internally represented as directed at an object component”; it “is exactly what makes consciousness subjective”. The cognitive 1PP adds a self-applied concept of a subject and is set aside. “Having MPS is a necessary condition for the strong (and the cognitive) 1PP, but not for the weak 1PP because the weak 1PP is itself a constituting factor for MPS.”
• Transparency and opacity (pp. 8, 10). “If parts of the conscious body-model become phenomenally opaque, that is, if they are experienced as a representation … the dimension of self-identification and consequently MPS can be weakened” (p. 8). From the autoscopic data, “there seems to be a continuum between transparency and opacity, which determines how realistically the content of a body representation is experienced and how strongly the dimension of self-identification is expressed” (p. 10).
• No substantial self (p. 8). MPS and other self-representations are “not static internal copies of some mysterious thing or individual substance (‘the’ self), but only ongoing processes of tracking and controlling global bodily properties”. Global properties are those of the system as a whole, like wetness, which no H2O molecule has.
• Box 1: necessity and sufficiency (p. 8).
  • “The existence of a conscious, transparent and global body-representation available for attentional access is a sufficient condition for MPS.”
  • “We claim that spatiotemporal self-location, self-identification and weak 1PP are necessary and sufficient for MPS. If there are further necessary conditions, then our claim is false.”
  • Agency: “The temporally preceding experience of agency and of global motor control (e.g. in childhood) causally enables MPS in practically all humans, but it is not causally necessary”. Out-of-body experiences and the experimental manipulations “demonstrate that agency only belongs to the causal background for MPS”. What constitutes MPS “could also take place in a disembodied, non-neural, artificial system possessing no effectors”.
• Partial against global ownership (pp. 9–10).
  • Somatoparaphrenia, after right temporo-parietal damage, “affects only the contralesional (mostly left) hand (or foot), and never ipsilesional body parts” (p. 9).
  • In the rubber-hand illusion the fake hand stroked in synchrony with the occluded real hand can produce felt touch, reported ownership and a displacement of felt hand position. “The RHI is abolished when the stroking is asynchronous” (p. 9).
  • Both “are only associated with changes in partial ownership and do not enable the investigation of MPS as the most fundamental sense of selfhood”. MPS is “not manipulated in healthy subjects during the RHI because these studies do not experimentally manipulate self-location, self-identification or the weak 1PP” (p. 9).
  • Neurons: fingertip fields in area 3b, larger fields in area 5, and VIP cells that may encode “the entire or large parts of the body surface”. “We argue that cells in area VIP and 5 are of importance for self-identification and other MPS-dimensions, whereas cells representing fingertips or hands are involved in partial ownership” (pp. 9–10). The vestibular system is added for global body representation (p. 10). This is a proposal, with no study of it cited.
• Neurology varies MPS along its dimensions (pp. 9–11, Box 2, Figs 1–2).
  • Autoscopic hallucination: a second own body is seen, but all three dimensions are normal and insight is preserved. Lesions centre on right parieto-occipital or temporo-occipital cortex (7 patients).
  • Out-of-body experience: self-location and the weak 1PP are at the illusory, usually elevated body, with “a sense of disembodiment”; self-identification is with the illusory body; all three dimensions and the strong 1PP are pathological, and there is usually no insight. Lesions mainly right temporo-parietal (n = 12).
  • Heautoscopy: self-location, weak 1PP and self-identification can sit at either body, at both, or alternate rapidly; patients report “being split in two selves”. Lesions mainly left temporo-parietal. On the authors’ reading this is “a brief double instantiation of MPS (two selves)” that “does not occur in any other form of autoscopic phenomenon” (p. 11).
  • The dimensions dissociate: an auditory weak 1PP can sit apart from the visual one, and in one stimulation case the patient had his visual weak 1PP at his body “but self-location 2 m behind his body as represented” (p. 12).
• Full-body illusions (pp. 11–12, Fig. 3). In Lenggenhager et al.’s set-up, participants see through a head-mounted display their own back, a fake body or an object stroked synchronously or asynchronously with their own back. With synchronous stroking “they felt as if the virtual body was their own (illusory self-identification) and showed drift towards it (illusory self-location)”. “Both full-body illusion measures were also observed for a fake body …, but not (or less so) for a rectangular object. The full-body illusion was abolished during asynchronous stroking.” In Ehrsson’s set-up, stroking at the unseen chest and in front of the camera induced “the experience of being at the position of the camera” behind the body. “Both studies revealed visual capture”: self-identification followed where the stroking was seen. The protocols induced neither an out-of-body experience nor an autoscopic hallucination, “but rather a state that is comparable to heautoscopy”, and “neither of them managed to manipulate what we have called the strong 1PP” (p. 12). Stratton’s 1899 mirror experiment is credited as the precursor.
• Conclusion (p. 12). “The reviewed clinical and experimental data show how a passive, multisensory and globalized experience of ‘owning’ a body is sufficient for minimal conscious selfhood.” “Agency might be a sufficient condition for MPS, but it does not belong to the metaphysically necessary part of the minimal supervenience base”. “Bodily agency is a causally enabling, but not a constitutive condition, for phenomenal selfhood.” Attentional access is speculated to be necessary for the move from MPS to the strong 1PP.

Claims

id	claim	strength	support
C1	The simplest form of selfhood (MPS) has three dimensions: global self-identification, self-location and a weak 1PP, jointly necessary and sufficient	asserted; Box 1 also allows that one may not be individually necessary	definitions, Box 1, p. 8
C2	Part ownership (rubber hand, somatoparaphrenia) and global ownership are distinct, and only the second bears on MPS	moderate as a conceptual sorting; the rubber-hand studies did not measure the MPS dimensions	p. 9, cited studies
C3	Part ownership and global self-identification rest on different neurons (hand fields against area 5, VIP and the vestibular system)	weak; a proposal from receptive-field sizes	pp. 9–10
C4	Autoscopic hallucination, heautoscopy and out-of-body experience differ in which MPS dimensions are disturbed, with right parieto-occipital, left and right temporo-parietal damage respectively	moderate, as a classification of reported cases	Box 2, Figs 1–2, small lesion series (7, 12, and one garbled count)
C5	Multisensory conflict shifts self-identification and self-location to where the stroking is seen, and asynchrony abolishes it	moderate, reported from two 2007 studies	pp. 11–12, Fig. 3
C6	Self-location can dissociate from the origin of the weak 1PP and from the location of the seen body	weak to moderate; one stimulation case and the two experiments	p. 12
C7	The degree of opacity of the body model sets how strongly self-identification is expressed	weak; read off the realism and insight of autoscopic phenomena	pp. 8, 10
C8	Agency is causally enabling but not constitutive of minimal selfhood, which could occur in a system without effectors	weak; inferred from adults whose agency was not exercised in the illusion, and conceptual	Box 1, p. 12

Concepts

• Minimal phenomenal selfhood (MPS). The conscious experience of being a self in its simplest form; a whole-body representation “functionally available for global control” (p. 8).
• Self-identification. “The degree to which an organism identifies with the content of a global body representation” (glossary).
• Self-location. “A determinate volume in space, normally localized within the bodily boundaries as represented”, within which the origin of the weak 1PP lies (glossary). Also temporal, which is not treated.
• Weak 1PP. The geometrical origin of an egocentric, usually visuospatial, model of reality.
• Strong 1PP. The system represented as directed at an object; for a phenomenal self as subject, a “phenomenal model of the intentionality relation” (p. 8).
• Partial against global ownership. Ownership of a body part against identification with the body as a whole.
• Global property. One that “can only meaningfully be ascribed to a given system as a whole” (p. 8).
• Causally enabling condition. A condition with a causal role that is “not strictly necessary” (Box 1), as against one in the minimal supervenience base.
• Agency (glossary). “Global motor control, including the subjective experience of action, control, intention, motor selection and the conscious experience of will.”

Connections

The paper puts Metzinger’s self-model theory to work on Blanke’s clinical series of out-of-body experience and heautoscopy, and on the 2007 full-body illusions. It takes the rubber-hand paradigm from Botvinick and Cohen (1998) and Tsakiris and Haggard (2005), and cites Gallagher’s How the Body Shapes the Mind and Pacherie’s phenomenology of action as the views on which agency is needed for a minimal self. The immunity literature (Shoemaker 1968; Mizumoto and Ishikawa 2005) is cited for the reading of out-of-body experience as an “error through misidentification” (Box 2). Metzinger’s “Self models” (LIT-450) is cited in the glossary and text.

Bearing on the record

• NOTE-372 and LIT-450. NOTE-372’s C6, “Body ownership can be manipulated by multisensory conflict and is the simplest form of self-awareness”, cites this paper. The paper supports the manipulation (C5) and narrows the “simplest form”: it is global ownership, and the rubber hand, the best-known manipulation of ownership, does not reach it (C2). NOTE-372’s own text already says “global body ownership”; the claim table’s wording is the looser one. NOTE-372’s C7, on phantoms in congenital limb absence, gets nothing here: Brugger’s chapter is cited only for hemibody ownership.
• THEORY-064 (LIT-568, NOTE-460). The paper is the self-model theory’s empirical programme for its most basic level. It also bears on the theory’s prediction, that a wholly opaque self-model would abolish selfhood. It offers a graded version (C7), that opacity weakens self-identification. Its evidence is the realism of autoscopic phenomena and insight into them, which are reports, so it does not answer NOTE-372’s open question of how transparency could be tested apart from reports of selfhood. It names no manipulation of opacity.
• THEORY-458 (LIT-453, NOTE-377). Gallagher’s minimal self has two parts, ownership and agency, which come apart. Blanke and Metzinger split ownership instead, into part and global, and make agency no part of the minimal self (C8). The two views disagree on what the minimal self is made of, not on any finding. Second, the paper calls out-of-body experience “an error through misidentification”. That is misidentification of the body one identifies with. On the immunity principle as NOTE-377 states it, “I” used as object can misidentify, so this is not a counterexample to THEORY-458’s immunity clause. The paper says, though, that the strong 1PP is also pathological in out-of-body experience. It does not say whether that reaches “I” as subject.
• LIT-1009 (NOTE-827). Haggard’s review holds that involuntary movement gives ownership without agency (its C1). That agrees with this paper’s thesis that a passive multisensory sense of owning a body suffices for minimal selfhood. The two reach it from opposite sides: Haggard by removing the motor command, Blanke and Metzinger by removing movement altogether.
• What C8 rests on. The thesis that agency is not constitutive is read off adults whose agency was intact and merely not used during the illusion, and patients who had agency before their lesions. The paper grants that agency “causally enables MPS in practically all humans”. So the evidence shows that MPS can be altered without agency playing a part at the time. It does not show that a system that never had agency could have MPS. That further claim (“a disembodied, non-neural, artificial system possessing no effectors”) is conceptual.
• Sibling filings. Lenggenhager et al. (2007), Botvinick and Cohen (1998), Apps and Tsakiris (2014) and Seth (2013) are filed on the same day. The first two are the primary studies behind C5 and C2. Their readings should check the paper’s descriptions of them, which this reading did not do.
• No instruction for machine-learning practice; nothing for the anthology. The remark on artificial systems is a conceptual possibility.

Limitations

• An opinion piece in a short format. No effect sizes, sample sizes or statistics are given for the full-body illusions. The lesion series are small (7 and 12, and one count unreadable in the extracted text).
• Box 1 is internally loose. The three dimensions are claimed “necessary and sufficient” under the heading “Necessary conditions that are not sufficient”. The next paragraph says “Perhaps one or more of them are not individually necessary.” The text also says agency “might be a sufficient condition for MPS” (p. 12), so there is more than one sufficient route on the authors’ own account.
• The dimensions blur in the experiments. The text labels Ehrsson’s felt location at the camera “illusory self-identification” (p. 12). The Figure 3 caption says the same set-up “diminished self-identification with the virtual body”. Being at the camera’s position is self-location or the weak 1PP’s origin on the paper’s own definitions.
• The text cites Box 2 for opacity (p. 8), but Box 2 does not discuss it; it discusses insight.
• The claim that the rubber hand leaves MPS untouched rests on what those studies did not measure, not on a measurement that found it unchanged.
• The authors review their own work. The theory is largely Metzinger’s, and the clinical series and one of the two experiments come from Blanke’s group.

Open questions

• Does the rubber-hand illusion really leave self-location and self-identification unchanged? It would take a study measuring the MPS dimensions during it.
• Can opacity of the body model be manipulated, apart from asking whether the experience feels real? The prediction of C7 needs it.
• Can the strong 1PP be manipulated experimentally? The paper predicts that multiple, spatially incongruent perspectives and prolonged exposure might do it (p. 12).
• Would a person with little or no history of bodily agency, such as someone with severe congenital paralysis, show full-body illusions? That would test C8 beyond what adult data can.