a self for the body

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A SELF FOR THE BODY

FRE DE RIQUE DE VIGNEMONT

Abstract: What grounds the experience of our body as our own? Can we rationallydoubt that this is our own body when we feel sensations in it? This article showshow recent empirical evidence can shed light on issues on the body and the self,such as the grounds of the sense of body ownership and the immunity to errorthrough misidentication of bodily self-ascriptions. In particular, it discusses howbodily illusions (e.g., the Rubber Hand Illusion), bodily disruptions (e.g., soma-toparaphrenia), and the multimodal nature of bodily self-knowledge challenge aclassic view of ownership and immunity that puts bodily sensations at its core.

Keywords: bodily sensations, body schema, body ownership, immunity to error,multimodality, Rubber Hand Illusion, self, somatoparaphrenia.

The body has always elicited strong opinions, either pro (e.g., Spinoza,

Nietzsche, Merleau-Ponty) or against (e.g., Plato, Descartes). Does thebody imprison and deceive the soul, distracting it from the acquisition of knowledge? Or does it ground our existence? In more contemporaryterms, could we be a disembodied brain in a vat or is embodimentconstitutive of the faculties of the mind? Surprisingly, in most discussions,little time is spent in analyzing what it is like to be embodied, in particularin relation to self-awareness. Here, I describe various philosophicalperspectives on the relation of the body and the self. I then focus on itspsychological and epistemological aspects and raise two main questions.First, what grounds the sense of body ownership (i.e., experiencing ones

body as ones own)? Second, what guarantees the immunity to errorthrough misidentication of bodily self-ascriptions (i.e., no possiblerational doubt that ones body is ones own)? A traditional method inphilosophy consists in appealing to thought experiments to solve thesetypes of question, but I show how recent scientic experiments canchallenge our classic assumptions on the role of bodily sensations forthe sense of body ownership and for bodily immunity.

1. The Body and the Self: A Panorama

In his short story The Notarys Nose , Edmond About (1862) described thetribulations of a notary who gets his nose cut off and who buys a new

r 2011 The AuthorMetaphilosophy r 2011 Metaphilosophy LLC and Blackwell Publishing LtdPublished by Blackwell Publishing Ltd, 9600 Garsington Road, Oxford OX4 2DQ, UK, and350 Main Street, Malden, MA 02148, USAMETAPHILOSOPHYVol. 42, No. 3, April 20110026-1068

r 2011 The AuthorMetaphilosophy r 2011 Metaphilosophy LLC and Blackwell Publishing Ltd


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nose from a poor water bearer and successfully grafts a bit of his armskin. Yet, the new nose behaves as if it were still part of the donors body.When the water bearer drinks too much, the notarys nose is red; when hestarves, it dwindles away; when he loses his arm from which the graft wasmade, the nose drops off altogether. This tale from the nineteen centuryhighlights a number of major questions about the relation of the bodyand the self that are still open today. What makes a nose ones own? Canone sell or buy a nose? Is the nose constitutive of a person? What groundsthe notarys experience of the new nose as his own? And can he doubt thatit is his own nose? Those questions are only a few examples of a widerange of issues about the body and the self from ontological, moral,psychological, and epistemological perspectives that I shall briey surveywith the help of a few key questions.

1.1. Ontological Issues

Is the self to the body merely what a captain is to his ship? Or is it more,and if so, what? According to a Cartesian view, the self is purely mental.Alternatively, one may argue that the body grounds the self, or that itanchors and individuates the self through time, thus guaranteeingpersonal identity. One may even go a step further and posit a relationof identity between the body and the self. Those questions aim atdetermining what the body is for the self. Alternatively, one may askwhich body has this specic relation to the self. In other words, we talk of our own body, but how to individuate it? As we shall see, it has beenproposed that ones own body is the body where one feels sensations, butone may as well claim that it is the body we care for and/or the body wedirectly control.

Here are some sample ontological questions:

Am I a body, or do I own a body?Is the self bodily?What role does the body play for personal identity?Which body is mine?

1.2. Ethical and Legal Issues

Biomedical research is booming. Crucial to all of this is the ability toobtain, store, and use parts of the human body taken from livingindividuals. These developments raise major issues concerning the moraland legal status of what one may call human biological materials. Thegeneral context of analysis is that the human body cannot be treated as asimple object upon which one has property rights, let alone as a mereinstrument. Though everyone agrees on the complexity of the moral andlegal status of the body, the views vary. In terms of the English Habeas


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Corpus Act (1675), the subject has full authority and unrestrictedproperty rights over her body. Alternatively, in terms of Roman lawand the model of the divine right of kings, the state owns the body anddecides its fate in order to protect society and the citizenry, while thesubject merely has usufruct of her body.

Here are some sample ethical and legal questions:

Can the body be owned? Can one have property rights to human bodyparts?If so, who owns the human body?Does the moral and legal status of the body vary whether it is the livingbody or the body after death, or whether it refers to separated tissuesor human uids (e.g., semen, saliva, blood)?

Can the body be commercialized like any object?

1.3. Psychological Issues

Our biological body directly strikes us as belonging to us. We are awareof our biological body as our own. But do we merely believe it or do wefeel it? According to the deationary conception of the sense of bodyownership, there may be only judgments of ownership, with no corre-sponding feeling of ownership. On the contrary, according to the ina-tionary conception, there is something it is like to experience our body asour own that goes beyond the mere experience of bodily properties. Ourbody is manifested to us in a form more primitive than beliefs or judgments, in the form of an immediate or pre-reective awareness of body ownership. But if there is such feeling of body ownership, whatgrounds it?

Here are some sample psychological questions:

Is there a positive phenomenology of myness?Is the sense of ownership similar for internal organs, face, and limbs?What is the functional role of the sense of ownership?

How is the sense of ownership related to (a) bodily sensations, (b)action, and (c) emotion?Can one feel body ownership toward any object besides ones biolo-gical body, no matter its shape and its location?Can one feel disownership toward ones biological body? If so, is thesense of disownership the mere result of the lack of sense of ownership?

1.4. Epistemological Issues

The self-ascription of a property is said to be immune to error throughmisidentication relative to the rst person (IEM) if one cannot bemistaken about the person who instantiates the propertynamely,


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oneselfwhen one has gained information about the property in theappropriate way. For instance, if I think that I am anxious because I feelanxious, my thought is IEM because introspection gives a privilegedinner access to my own mental life that I do not have for other peoplesmental life. But if I think that I am anxious because my psychoanalysttold me so, my thought is not IEM. Indeed, the psychoanalyst may haveconfused me with another patient, who is the person suffering fromanxiety. One can be mistaken about the psychological property oneascribes to oneself, but one cannot be mistaken about the person whoinstantiates the psychological property. Most accounts of immunity toerror through misidentication have focused on self-ascriptions of mental states (Shoemaker 1968; Wright 1998; McGinn 1983; Peacocke1999; Pryor 1999). But is immunity an epistemic property restricted to acertain class of psychological self-ascriptions or does it apply as well toself-ascriptions of bodily properties? By bodily self-ascriptions, I do notmean the ascription of bodily sensations. Bodily sensations are mentalstates, like emotions, beliefs, or desires. By bodily ascription, I mean theascription of bodily properties (e.g., body size, weight, posture, and thelike).

Here are some sample epistemological questions:

Are bodily self-ascriptions IEM?What are the appropriate grounds that can secure bodily immunity?

Do self-ascriptions of bodily properties display the same type of immunity as self-ascriptions of mental states?Does bodily immunity reveal the bodily nature of the self?

To conclude, questions about the body and the self have long beenconsidered to be beyond the reach of experimental studies. This is true of some of them, but over the past ten years research in cognitive science hasyielded a vast array of exciting discoveries and provocative hypothesesabout bodily awareness and self-awareness. Here, I shall illustrate howthe dialogue between philosophy and cognitive science can be fruitful forboth domains. On the one hand, confrontation with empirical ndingssheds new light on long-standing conceptual issues about the body andthe self, helps philosophers to forge and sharpen new conceptual frame-works for the investigation of bodily self-awareness, and raises newphilosophical puzzles. However, empirical results provide only partialor indirect replies to questions raised in philosophy. Philosophicaltheories and conceptual tools are thus needed for the perspicuousinterpretation of empirical data and their systematization.

2. Bodily Sensations and Bodily Ownership

One strategy for answering some of the questions outlined above is tocompare experiences of ones own body and experiences of other peoples




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bodies. The underlying assumption is that what is specic to theexperiences of ones own bodywhether it is the specic way oneperceives it, one affectively reacts to what happens to it, or one controlsitmay indicate which body is ones own and which body one experi-ences as ones own. Here, I shall limit myself to analyzing the differenttypes of perceptual experiences of ones body and of other bodies.

We have a privileged internal access to our own body that we do nothave for other bodies. Unlike other physical objects, our body is ex-perienced not only from the outside (i.e., through external senses) but alsofrom the inside (i.e., through body senses). 1 We do not feel bodilysensations in bodies other than our own, whereas we see many bodies.A traditional conception of body ownership thus relates bodily sensationsand body ownership at various levels:

(a) At the ontological level of body ownership (e.g., Locke 1689):ones own body consists in the body in which one feelssensations.

(b) At the psychological level of the sense of body ownership (e.g.,Brewer 1995; Cassam 1997; Dokic 2003; Martin 1995; Bermu-dez 1998): the body that one experiences as ones own is thebody that one experiences from the inside.

(c) At the level of the epistemic properties of judgments of bodyownership (e.g., Evans 1982; Brewer 1995; Cassam 1997; Ber-mudez 1998): bodily self-ascriptions are IEM if they aregrounded in bodily experiences.

At this point I shall leave aside the ontological view to focus on the otherviews. On the psychological view, the sense of body ownership isgrounded in bodily experiences such as the sense of pressure, the senseof posture, and the sense of balance (i.e., body senses). There are twoways to interpret this theory. According to the informational account,bodily experiences ground the sense of ownership because the body sensesare characterized by a privileged informational/causal link to ones body,and to no other bodies. For example, I cannot have access to the postureof another body through proprioception. The body that one experiencesas ones own is the body from which one receives internal information(e.g., through proprioception). Alternatively, according to the spatialaccount, what grounds the sense of ownership is not the fact that one hasaccess to the bodily property from the inside but the fact that one localizesthe bodily property within the spatial representation of ones own body.When I feel a bodily sensation, I do not feel it in one body as opposed to

1 The distinction between from the inside and from the outside is taken for granted here.For sake of simplicity, I assume that bodily experiences are from the inside if they consist in

bodily sensations, whereas bodily experiences are from the outside if they consist in ordinaryperceptual experiences (e.g., visual experiences).




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another body. I feel it in my own body. The body that one experiences asones own is the body in which one spatially ascribes sensations. 2 On bothaccounts, vision is disqualied as a possible ground of the sense of ownership. As Brewer says, the visual body, that is, the body from theoutside, does not bear the stamp of ownership (1995, 305). On the onehand, vision carries information about more than ones own body. On theother hand, the property can be localized outside the representation of theboundaries of ones body. When one sees a red spot on ones hand, onesees it on one hand as opposed to many other hands.

The dichotomy between two types of perceptual experience, eitherfrom the inside or from the outside, is also at the core of the epistemo-logical view, which claims that the two types of perceptual experience leadto two classes of bodily judgment with distinct epistemic properties. Inparticular, bodily self-ascriptions based on bodily experiences are said tobe IEM because bodily experiences give a privileged inner access to onesbodily states. For instance, on the basis of proprioception, I may bemistaken about my bodily posture (e.g., my legs are not crossed), but Icannot rationally doubt that those are my legs that I feel are crossed.Proprioceptive experiences sufce to justify bodily self-ascriptions suchthat no intermediary process of self-identication is required. The judgment my legs are crossed is not grounded in the judgment thoselegs are crossed and in the identication those legs are mine. Bycontrast, as Wittgenstein noted (1958), I can see an arm broken, but this

does not entitle me to directly conclude that my own arm is broken. Itmight be another persons arm that is intermingled with mine. I may bemistaken about whose arm is broken because I can see my arm as well asmany other arms. There is a gap between visually knowing that a body isF and visually knowing that it is my own body that is F, a gap that needsto be fullled with the help of self-identication.

To conclude, there seems to be a dichotomy between two well-denedtypes of perceptual experience of ones body, from the inside and from theoutside, with distinct psychological properties (stamp of ownership ornot) and distinct epistemic properties (bodily immunity or not). I shall

now rene this view in the light of empirical phenomena. In section 3,I show how the analysis of some disorders and illusions of bodilyself-awareness contributes to our understanding of the relation betweenbodily experiences and the sense of body ownership. In section 4, I revisethe dichotomy between the perception of the body from the inside andfrom the outside in the light of pervasive multimodal effects, and assesstheir consequences for bodily immunity. I do not go into detail each time

2 Arguably, the specic type of spatial content that characterizes bodily experiences

ultimately derives from the privileged informational/causal relation between the body sensesand ones body.




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but instead sketch how cognitive science can improve our understandingof the sense of body ownership and bodily immunity. 3

3. The Grounds of the Sense of Ownership

3.1. This Is My Hand

Can one experience ownership toward an object extraneous to onesbiological body? The reply is yes, as shown by a bodily illusion recentlydiscovered, the Rubber Hand Illusion (RHI). The RHI has become themain experimental design for articially manipulating the sense of bodyownership in healthy individuals. Participants sit with their arm restingon a table, hidden behind a screen, while looking at a fake hand in frontof them. An experimenter then simultaneously strokes with two paint-brushes both the participants biological hand and the fake hand. Theillusion is fourfold: (i) participants feel as if they were touched on therubber hand; (ii) they feel as if the rubber hand were their own hand; (iii)they mislocalize their hand in the direction of the rubber hand (i.e.,proprioceptive drift); (iv) they emotionally react when the rubber hand isthreatened or hurt as if it were their own hand that was in danger.Although there are some disagreements about the correct interpretationof the RHI, one may conclude that one can experience an object as onesown despite the fact that it is not spatially connected with ones biologicalbody and that one knows that it is merely a rubber hand: I found myself looking at the dummy hand thinking it was actually my own (qtd.Botvinick and Cohen 1998, 756).

Hence, it seems that an object that is only seen can bear the stamp of ownership. This result questions the relation between bodily sensationsand the sense of ownership. More particularly, I shall argue that the RHIrefutes the informational account of ownership, but not the spatialaccount. One can indeed explain the sense of ownership of the rubberhand in terms of the spatial content that assigns a specic location to thebodily property within a representation of the space of ones body.

In the RHI, participants do not receive tactile information from the

rubber hand (i.e., they do not have tactile receptors on the rubber handthat convey tactile signals to the brain), they receive it from theirbiological hand that is touched in synchrony. Hence, it is not necessaryto receive information from the inside (e.g., through the sense of pressure)to experience a body part as ones own. Yet, we are not entitled toconclude on the sole basis of these results that the sense of ownership iscompletely independent of bodily experiences and that it is grounded in afurther mechanism, still to be determined. What is interesting in the RHIis that the participants localize the sensation of pressure in the rubber

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For a detailed account of the sense of ownership, see de Vignemont 2007, 2010b. For adetailed account of bodily immunity, see de Vignemont forthcoming.




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hand, not the biological hand. The sense of ownership of the rubber handis thus compatible with the spatial account. If the sense of body owner-ship is indeed grounded in the spatial ascription of bodily experiences, it isno surprise that participants experience the rubber hand as their own.Nonetheless, the RHI offers a new insight on the spatial account of thesense of ownership. In particular, it reveals that pressure is localizedwithin a spatial representation of the body that is based not only on touchbut also on vision. One needs thus to rene the spatial account of thesense of ownership to take into consideration the multimodality of therepresentation of the body space. I shall come back to this account later.

3.2. This Is Not My Hand

Not only can we experience as our own an extraneous object, we can alsoexperience our own body as alien. Although the sense of body ownershipmay appear as a given, various psychiatric or neurological conditionsindeed highlight the possibility of losing the sense of ownership of onesbody. For example, patients suffering from the psychiatric disorder of depersonalization experience a general alteration of their relation to theself, as revealed by anomalous bodily experiences, emotional numbing,sensation of alienation from surroundings, and anomalous subjectiverecall (Sierra et al. 2005). I dont know who I am, of course I am nnnn butI feel like a robot, like I am listening to someone else talking, like I amlooking at myself from the outside, but it is not another voice or body, itis mine, it is me, it just doesnt feel like it (qtd. Baker et al. 2003, 432).

In particular, patients often feel as if their body did not belong to themor as if it had disappeared, leading them to compulsively touch their bodyand pour hot water on it to reassure themselves of their bodily existence.Similarly, following a brain lesion or epileptic seizure, patients withsomatoparaphrenia (also sometimes called asomatognosia or alien handsign) deny ownership of one of their limbs, and can even attribute it toanother individual (Vallar and Ronchi 2009).

Examiner: Whose arm is this? AR: Its not mine. Ex: Whose is it? AR: Its my

mothers. Ex: How on earth does it happen to be there? AR: I dont know. Ifound it in my bed. Ex: How long has it been there? AR: Since the rst day.Feel, its warmer than mine. The other day too, when the weather was colder, itwas warmer than mine. Ex: So, where is your left arm? AR: Its under there(indenite gesture forwards) [ . . . ] Look, its queer, but thats how it is. Justfancy nding your sons arm in your bed. (Qtd. Bisiach, Rusconi, and Vallar1991, 1030)

Whereas patients with depersonalization are aware that their bodilyalienation is just an illusion, patients with somatoparaphrenia are con-vinced that the limb does not belong to them, and they maintain theirdelusional belief despite correction: Feinberg: Suppose I told you thiswas your hand? Mirna: I wouldnt believe you (qtd. Feinberg et al. 2005,




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that they felt the touch but did not know where. However, disownershipsyndromes may not be a fatal objection against the spatial account if there are several types of representation of the body space, and only oneof them grounds the sense of ownership. I shall briey develop thisargument here.

Arguably, one single type of body representation cannot sufce toaccount for the diversity of bodily aspects (e.g., semantic, emotional,spatial, motor, tactile, visual, proprioceptive, and so on) and the varietyof bodily disorders (e.g., autotopagnosia, phantom limb, somatoparaph-renia, anorexia nervosa, body-specic aphasia, personal neglect, and soon). In particular, one may distinguish between the representation of bodily information exploited for action (i.e., body schema) and therepresentation of bodily information used by perception (i.e., bodyimage) (Paillard 1999; Gallagher 2005; de Vignemont 2010a). If thereare several types of body representation, then the alien hand can berepresented at one level but not at another. Furthermore, one may suggestthat it is the impaired body representation that is responsible for the lackof ownership. A careful study of somatoparaphrenia can thus help us todetermine which body representation is disrupted, and eventually whichbody representation grounds the sense of ownership.

I shall not go into details here, but some evidence points toward adisruption of the body schema in somatoparaphrenia. Interestingly, mostsomatoparaphrenic patients are either paralyzed or suffer from the

anarchic hand syndrome (they cannot control their alien hand). Forexample, a patient during epileptic seizure felt his leg as alien andimmediately fell down. One possible interpretation is that his leg wasno longer represented within his body schema, which led the patient bothto fall and to feel that the leg did not belong to him (Elson and Schau ble2004). I propose that the sensorimotor body representation that carriesinformation about the long-term properties of ones own body necessaryfor action is at the source of the sense of ownership. Roughly speaking,the body that you represent for acting is the body that you experience asyour own. In somatoparaphrenia, the alien limb is no longer repre-

sented within this sensorimotor representation of the body space, thuspreventing the touch from being localized on the hand at the sensor-imotor level, and the hand from feeling like ones own.

To conclude, the analysis of illusory and disrupted ownership experi-ences has deepened our understanding of the relation between bodilyexperiences and the sense of ownership. In a nutshell, the sense of bodyownership can be at odds with the body that one experiences from theinside. I have shown that the Rubber Hand Illusion and somatopara-phrenia argue against the informational account of the sense of owner-ship. Yet, they can t within the framework of the spatial account.Nonetheless, further arguments and details need to be provided if onewants to make a case for the spatial account of the sense of ownership.




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One needs to develop a theory of the spatial ascription of bodilyexperiences that takes into account the role of vision and action inshaping the representation of the bodily space. It is only if one takes intoaccount the recent empirical literature on body representations that onecan offer a full-eshed theory of bodily space and the sense of bodyownership.

4. The Grounds of Bodily Immunity

I shall now approach the link between bodily experiences and ownershipat the epistemological level. I shall analyze the various ways empiricalphenomena could enrich our understanding of immunity to error throughmisidentication before focusing on the issue of multimodal bodily self-knowledge.

First, in order to question the hypothesis of immunity to error, onemay look at recent technological developments and prospects thatchallenge the very idea that one is connected only to ones biologicalbody. Patients who are completely paralyzed can play ping-pong on acomputer screen. Artists like Stellarc can incorporate a prosthetic thirdarm that moves at will. What used to be mere thought experiments maysoon become reality. The anatomical constraints that secure the causalchain between bodily experiences and ones body might be overridden inthe future if, for instance, ones brain is connected to another individuals

body. One would then directly experience from the inside anothers bodilystates and postures. If so, knowing that the arms are crossed via pro-prioception would no longer guarantee that those crossed arms are onesown arms. In this futuristic scenario, bodily self-ascriptions groundedin bodily experiences are not IEM (immune to error through misidenti-cation).

A second way to empirically address the issue of bodily immunity is tolook for bodily misidentication in judgments that are grounded in bodilyexperiences. If such cases exist, then bodily self-ascriptions are not IEM.One may suggest, for instance, that the RHI (Rubber Hand Illusion) and

somatoparaphrenia constitute such cases (e.g., Mizumoto and Ishikawa2005). In both cases, one misidenties whose hand it is, whether one self-attributes an external hand or attributes ones own hand to anotherindividual. However, not just any case of misidentication can falsifythe hypothesis of immunity to error, and in particular neither the RHInor somatoparaphrenia can challenge the fact that bodily experiencesguarantee bodily immunity. The hypothesis of bodily immunity claimsthat if the ownership judgment derives from the appropriate way of gaining information about the bodily property, namely, the senses of posture, balance, and pressure, then it is IEM. But the way of gainingbodily knowledge is not appropriate in the RHI. Indeed, it is vision thatgives the information that the bodily property is instantiated, not




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proprioception or touch. That is why the RHI is characterized in terms of visual capture of touch and proprioception. And in this case, vision doesnot guarantee bodily immunity. As for somatoparaphrenia, the patientshave the appropriate grounds that guarantee the immunity of bodily self-ascriptions (e.g., they have tactile experiences), if self-ascriptions are to bemade. But the mere presence of appropriate grounds does not sufce toguarantee that one does make those self-ascriptions. Roughly, it is notbecause one has plenty of good reasons to believe that p that one believesthat p. And it is not because one does not believe that p that one does nothave good reasons for believing that p. Hence, the patients may have theappropriate grounds to make the judgment that this is ones own hand,but that does not necessarily imply that one makes such a judgment. Andthe fact that the patients do not make the ownership judgment does notchallenge the validity of the grounds. The patients may indeed have otherreasons that they think of as defeating their grounds. Hence, somatopar-aphrenia and the RHI have no relevance for bodily immunity.

Finally, what is perhaps the most interesting and promising way toempirically address bodily immunity is to focus on the grounds of bodilyself-knowledge. One important move in the discussion of immunity toerror has been to acknowledge that immunity applies not to propositionsper se but to thoughts made upon specic grounds. In principle, any self-ascription can be IEM if the subject has gained information about theproperty in the appropriate way. This allows not only psychological self-

ascriptions but also bodily self-ascriptions to be IEM. But what are theappropriate grounds that secure bodily immunity? It is generally assumedthat the body senses (e.g., touch, proprioception, and sense of balance)guarantee bodily immunity. However, recent empirical ndings haveshown that the normal way of gaining bodily self-knowledge is not viathe body senses per se but rather via the integration of body senses andvision. Bodily self-knowledge is primarily multimodal. But if bodily self-ascriptions are grounded not only in proprioception, which secures bodilyimmunity, but also in vision, which is not supposed to secure bodilyimmunity, are bodily self-ascriptions still IEM?

For a long time, most research on perception has studied each sensorymodality in isolation. However, not only do we experience the worldthrough various senses at the same time, those senses also interact witheach other. Then information from one modality impacts another suchthat the information reorganizes its perceptual experience. Plurimodalintegration can imply the resolution of conicts between the differentkinds of information, and it can even sometimes lead to perceptualillusions. For example, in the ventriloquism effect, the absence of seen lipmovement alters the apparent location of speech sounds. Cross-modaleffects can be found between all modalities. In particular, vision, pro-prioception, and touch can interfere with each other. For presentpurposes, I shall present just a single example.




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reported that one day he stepped onto a bus and noticed a man wholooked like a shabby pedagogue, whereas he was actually seeing himself ina large mirror at the far end of the bus. But there are some circumstanceswhen one directly sees ones body and one cannot doubt that it is onesown body that one sees. 5 Whether vision guarantees bodily immunity ornot depends on the visuo-spatial perspective (i.e., the angle and distancefrom which the body is seen). If you see a body far away in the middle of aforest, it is highly unlikely that this body is your own. But if you see a nosewhen you shut one eye and look down at a sharp angle, the nose can onlybe your own, not anybody elses. This is due to the fact that therepresentation of the body from this specic visuo-spatial perspective isself-specic. Put another way, it is anatomically impossible that it couldbe another individuals nose that you see from this angle at this distance.Hence, one should not automatically disqualify vision as a valid groundfor bodily immunity.

Still, there are some casesactually, most caseswhere vision doesnot guarantee bodily immunity. For instance, when I see my hand on thetable, it could just as well be anothers hand. And if this visual infor-mation is integrated with proprioceptive information about the locationof my hand, then my judgment my hand is on the table is based onmixed grounds, only partially IEM. If we defend the view that bodily self-ascriptions are IEM if and only if they are exclusively based on groundsthat guarantee bodily immunity, then my judgment is not IEM. But there

is no principle that commits us to defend this strong view of bodilyimmunity. Rather, we need to understand the basic mechanisms of multisensory integration if we want to assess the immunity of visuo-proprioceptive judgments. In particular, we need to determine if multi-modal integration involves self-identication. Indeed, it is only if there isidentication of the subject that there can be errors through misidenti-cation relative to the subject.

For two sensory signals to be integrated, they need to be assigned to thesame individual (i.e., assumption of unity; cf. Welch and Warren 1986).Thus what is required is to select the relevant sensory signals that come

from a common source, and to segregate them from those that come from adifferent source. In other words, it is not adaptive for the perceptual systemto integrate proprioceptive information about ones hand with visualinformation about anothers hand. Rather, what is needed is to makesure that both types of information are about the same hand in order toincrease reliability of the perceptual judgment. The question, then, iswhether the assumption of unity requires self-identication.

On one interpretation, one would need rst to identify whose hand oneis seeing before integrating the visual information with the proprioceptive

5

In addition, some visual experiences of the external world can guarantee bodilyimmunity. See Evans 1982, Bermudez 1998, and de Vignemont 2010a for more details.




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information, and visuo-proprioceptive integration would be identica-tion-dependent. This interpretation, however, is misleading. Multimodalintegration does not require that the subject feel that her hand is F, seethat x is F, judge that x is her hand, and integrate what she feels with whatshe sees. On the one hand, multimodal integration occurs very early on inthe perceptual process, at a stage where raw modality-specic sensorysignals are not available to the subject. Rather than identication, onemay talk of a subpersonal process of assignment (Deneve and Pouget2004). On the other hand, there is no need to rst identify the source todetermine that the sensory signals come from the same source. It sufcesto compare the sensory signals themselves and the information they carry.For example, if they occur at the same time and carry information aboutthe same location within the same frame of reference, then it is likely thatthey carry information about the same individual. The reliability of theassumption of unity depends on the number of properties that arecongruent across the sensory signals. Hence, the visual system does nothave to identify the seen body as ones own body. Rather, the propertiesof the seen body are compared with the properties of the felt body (e.g.,location, posture), and if they are similar enough, the visual andproprioceptive signals are melted into a multimodal perceptual experienceof ones hand.

Under normal circumstances, the process of assignment to a commonsource is reliable. The fact of the matter is that we do not integrate visual

information from other peoples bodies with proprioceptive informationfrom our own body, except in some articially induced bodily illusions.This does not mean, however, that the assignment process is infallible. Itmay happen that visual information about a rubber hand is integratedwith proprioceptive information about ones hand because visual infor-mation is mistakenly assigned to the same hand as proprioceptiveinformation. Consequently, there can be errors. But they are not errorsthrough misidentication.

To conclude, one should not accept the classical dichotomy betweenimmunity-preserving body senses and vulnerable vision. Nor should one

assume the exclusive thesis such as only the judgments that are exclusivelygrounded in body senses are immune to error. Rather, I propose to extendthe list of grounds appropriate for bodily IEM to include visualexperiences of the body from a self-specic perspective and bodilyexperiences resulting from the integration of vision and body senses.Only sensory signals assigned to a common source are indeed integratedwith each other, and the assignment to a common source results from asubpersonal comparative process that does not depend on self-identica-tion. Consequently, bodily immunity is preserved in integration-basedbodily self-ascriptions. It might happen that the assignment process fails,but this cannot be assimilated to an error through misidenticationrelative to the rst person.




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Conclusion

In this article I have opened new avenues of dialogue between philoso-

phers and scientists working on the body and the self. In particular, I havediscussed how recent empirical evidence on such topics as the RubberHand Illusion, somatoparaphrenia, and the multimodal nature of bodilyself-knowledge can help philosophers to revise and rene a classic view of ownership and immunity that puts bodily sensations at its core.

New York UniversityDepartment of Philosophy5 Washington PlaceNew York, NY 10003

USA [email protected]

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