Fission and Split Brains

If we were to connect two individuals’ brains together, how would this affect the individuals’ conscious experiences? In particular, it is possible for two people to share any of their conscious experiences; to simultaneously enjoy some token experiences while remaining distinct subjects? The case of the Hogan twins—craniopagus conjoined twins whose brains are connected at the thalamus—seems to show that this can happen. I argue that while practical empirical methods cannot tell us directly whether or not the twins share conscious (...) experiences, considerations about the locality of content processing in the brain entails that they most likely do so. (shrink)

In der Diskussion um personale Identität nehmen die einflussreichen Arbeiten Derek Parfits eine Sonderstellung ein, insofern Parfit nicht bestrebt ist, eines der gängigen Identitätskriterien zu verteidigen, sondern vielmehr behauptet, dass unsere alltäglichen wie philosophischen Vorstellungen von personaler Identität unrettbar inkohärent sind und deshalb aufgegeben werden sollten. In seinem Beitrag beleuchtet Sascha Settegast die verschiedenen Argumente, die Parfit für diese provokante These vorbringt, und unternimmt insbesondere den Versuch einer systematischen Dekonstruktion der wichtigsten Gedankenexperimente Parfits, die zeigen soll, dass sich diese Gedankenexperimente (...) auf eine Weise auflösen lassen, die unsere alltäglichen Intuitionen über personale Identität intakt belässt. Settegast entwickelt dabei die Grundzüge einer Konzeption personaler Identität, die sich einerseits von den gängigen neo-lockeanischen und animalistischen Ansätzen abgrenzt und andererseits bewusst an den zeitgenössischen Neo-Aristotelismus in der Ethik anknüpft, wie er etwa bei Philippa Foot und Michael Thomp-son anzutreffen ist. Die diachrone numerische Identität menschlicher Personen gründet nach Settegasts Auffassung darin, dass der Verlauf ihres Lebens eine zeitliche Einheit aufweist, die dadurch bedingt ist, dass ihre Lebensführung die menschliche Lebensform auf eine individuell charakteristische Weise exemplifiziert. Insofern dies aber nur durch Kultivierung der Tugen-den zu erreichen ist, handelt es sich laut Settegast bei personaler Identität letztlich nicht um eine Tatsache, die einfach vorliegt oder nicht, sondern um eine Aufgabe, die uns als Menschen gegeben ist und wesentlich darin besteht, in bewusster Orientierung auf das gute Leben hin ein stabiles, sich zeitlich durchhaltendes Selbst allererst auszubilden. (shrink)

Elizabeth Schechter explores the implications of the experience of people who have had the pathway between the two hemispheres of their brain severed, and argues that there are in fact two minds, subjects of experience, and intentional agents inside each split-brain human being: right and left. But each split-brain subject is still one of us.

Lynne Baker's concept of a first-person perspective is not as clear and straightforward as it might seem at first glance. There is a discrepancy between her argumentation that we have first-person perspectives and some characteristics she takes first-person perspectives to have, namely, that the instances of this capacity necessarily persist through time and are indivisible and unduplicable. Moreover, these characteristics cause serious problems concerning personal identity.

Given reductionism about people, personal persistence must fundamentally consist in some kind of impersonal continuity relation. Typically, these continuity relations can hold from one to many. And, if they can, the analysis of personal persistence must include a non-branching clause to avoid non-transitive identities or multiple occupancy. It is far from obvious, however, what form this clause should take. This paper argues that previous accounts are inadequate and develops a new proposal.

Jason Bowers and Meg Wallace have recently argued that those who hold that every individual instantiates a ‘haecceity’ are caught up in a Euthyphro-style dilemma when confronted with familiar cases of fission and fusion. Key to Bowers and Wallace’s dilemma are certain assumptions about the nature of metaphysical explanation and the explanatory commitments of belief in haecceities. However, I argue that the dilemma only arises due to a failure to distinguish between providing a metaphysical explanation of why a fact holds (...) vs. a metaphysical explanation of what it is for a fact to hold. In the process, I also shed light on the explanatory commitments of belief in haecceities. (shrink)

Martine Nida-Rümelin has argued recently for subject-body dualism on the basis of reflections on the possibility of survival in fission cases from the literature on personal identity. The argument focuses on the claim that there is a factual difference between the claims that one or the other of two equally good continuers of a person in a fission case is identical with her. I consider three interpretations of the notion of a factual difference that the argument employs, and I argue (...) that on each of them the argument either begs the question or is unsound. (shrink)

In “The Argument for Subject Body Dualism from Transtemporal Identity Defended” (PPR 2013), Martine Nida-Rümelin (NR) responded to my (PPR 2013) criticism of her (2010) argument for subject-body dualism. The crucial premise of her (2010) argument was that there is a factual difference between the claims that in a fission case the original person is identical with one, or the other, of the successors. I argued that, on the three most plausible interpretations of ‘factual difference’, the argument fails. NR responds (...) that I missed the intended, fourth interpretation, and that, in any case, with an additional assumption, the argument on the third interpretation goes through. I argue that the fourth interpretation, while insufficient as stated, reveals an assumption that provides an independent argument, namely, that in first person thought about future properties we have a positive conception of the self that rules out having empirical criteria of transtemporal identity. I argue that the considerations offered for this thesis fail to establish it, and that we do not bring ourselves under any positive conception in first person thought. I argue also that on the third interpretation, the first premise of the argument is inconsistent with the necessity of identity. (shrink)

This is a critical review of Raymond Martin's 'Self-Concern' (1998), focusing especially on his criticism of Parfit's use of fission thought-experiments and his own 'fission rejuvenation' thought-experiment.

Derek Parfit’s argument against the platitude that identity is what matters in survival does not work given his intended reading of the platitude, namely, that what matters in survival to some future time is being identical with someone who is alive at that time. I develop Parfit’s argument so that it works against the platitude on this intended reading.

David Lewis defends the following "non-circular definition of personhood": "something is a continuant person if and only if it is a maximal R-interrelated aggregate of person-stages. That is: if and only if it is an aggregate of person-stages, each of which is R-related to all the rest (and to itself), and it is a proper part of no other such aggregate." I give a counterexample, involving a person who is a part of another, much larger person, with a separate mental (...) life. I then offer an easy repair, which preserves the virtues of Lewis's definition without introducing any new vices. (shrink)

Imagine that you and a duplicate of yourself are lying unconscious, next to each other, about to undergo a complete step-by-step exchange of bits of your bodies. It certainly seems that at no stage in this exchange of bits will you have thereby switched places with your duplicate. Yet it also seems that the end-result, with all the bits exchanged, will be essentially that of the two of you having switched places. Where will you awaken? I claim that one and (...) the same person possesses both bodies, occupies both places and will experience both awakenings, just as a person whose brain has been bisected must at once experience both of the unconnected fields of awareness, even though each of these will falsely appear to him as the entirety of his experience. I also claim that the more usual apparent boundaries of persons are as illusory as those in brain bisection; personal identity remains unchanged through any variation or multiplication of body or mind. In all conscious life there is only one person - I - whose existence depends merely on the presence of a quality that is inherent in all experience - its quality of being mine, the simple immediacy of it for whatever is having experience. One powerful argument for this is statistical: on the ordinary view of personhood it is an incredible coincidence for you (though not for others) that out of 200,000,000 sperm cells the very one required on each occasion for your future existence was first to the egg in each of the begettings of yourself and all your ancestors. The only view that does not make your existence incredible, and that is not therefore (from your perspective) an incredible view, is that any conscious being would necessarily have been you anyway. It is a consequence that self-interest should extend to all conscious organisms. (shrink)

Recent work in personal identity has emphasized the importance of various conventions, or ‘person-directed practices’ in the determination of personal identity. An interesting question arises as to whether we should think that there are any entities that have, in some interesting sense, conventional identity conditions. We think that the best way to understand such work about practices and conventions is the strongest and most radical. If these considerations are correct, persons are, on our view, conventional constructs: they are in part (...) constituted by certain conventions. A person exists only if the relevant conventions exist. A person will be a conscious being of a certain kind combined with a set of conventions. Some of those conventions are encoded in the being itself, so requiring the conventions to exist is requiring the conscious being to be organized in a particular way. In most cases the conventions in question are settled. There is no dispute about what the conventions are, and thus no dispute about which events a person can survive. These are cases where we take the conventions so much for granted, that it is easy to forget that they are there, and that they are necessary constituents of persons. Sometimes though, conventions are not settled. Sometimes there is a dispute about what the conventions should be, and thus a dispute about what events a person can survive. These are the traditional puzzle cases of personal identity. That it appears that conventions play a part in determining persons’ persistence conditions only in these puzzle cases is explained by the fact that only in these cases are the conventions unsettled. Settled or not though, conventions are necessary constituents of persons. (shrink)

It seems plausible that (i) how much punishment a person deserves cannot be affected by the mere existence or nonexistence of another person. We might have also thought that (ii) how much punishment is deserved cannot increase merely in virtue of personal division. I argue that (i) and (ii) are inconsistent with the popular belief that, other things being equal, when people culpably do very wrong or bad acts, they ought to be punished for this—even if they have repented, are (...) now virtuous, and punishing them would benefit no one. Insofar as we cannot deny (i), we are either forced to abandon the popular belief in desert, or else allow that personal division could, as I put it, “multiply desert.” Some may not find the latter, considered by itself, troubling. But I argue that the thesis that division multiplies desert faces a potentially serious problem, which arises in the context of personal fusion. It is difficult to see how to maintain a particular family of desert views in light of the cases here presented. (shrink)

Abstract: Those who endorse the Psychological Continuity Approach (PCA) to analyzing personal identity need to impose a non-branching constraint to get the intuitively correct result that in the case of fission, one person becomes two. With the help of Brueckner's (2005) discussion, it is shown here that the sort of non-branching clause that allows proponents of PCA to provide sufficient conditions for being the same person actually runs contrary to the very spirit of their theory. The problem is first presented (...) in connection with perdurantist versions of PCA. The difficulty is then shown to apply to endurantist versions as well. -/- . (shrink)

Abstract: In this paper, I argue that standard psychological continuity theory does not account for an important feature of what is important in survival – having the property of personhood. I offer a theory that can account for this, and I explain how it avoids two other implausible consequences of standard psychological continuity theory, as well as having certain other advantages over that theory.

According to conventional wisdom, the split-brain syndrome puts paid to the thesis that consciousness is necessarily unified. The aim of this paper is to challenge that view. I argue both that disunity models of the split-brain are highly problematic, and that there is much to recommend a model of the split-brain—the switch model—according to which split-brain patients retain a fully unified consciousness at all times. Although the task of examining the unity of consciousness through the lens of the split-brain syndrome (...) is not a new one—such projects date back to Nagel’s seminal paper on the topic—the time is ripe for a re-evaluation of the issues. (shrink)

Most philosophers in the analytical philosophy answer the question what personal identity is in psychological terms. Arguments for substantiating this view are mainly based on thought experiments of brain transfer cases and the like in which persons change brains. However, in these thought experiments the remaining part of the body plays only a passive part. In this paper I argue that the psychological approach of personal identity cannot be maintained, if the whole body is actively involved in the analysis, and (...) that the body is an intrinsic part of what I am as a person. (shrink)

Parfit’s well known book, Reasons and Persons, argues, among other things, that ‘what matters’ in regard to ‘survival’ is not personal identity but something he calls ‘relation R.’ On this basis, plus other considerations, he rejects the ‘Self-interest’ theory as to what should be our aim in life. Here I show, or try to show, that his over-all argument is seriously defective. In particular, he fails to prove that personal identity is not what matters for survival.

(No abstract is available for this citation).