Fission and Split Brains

Consider the conscious states of a single subject at a time. Arguably, split-brain cases show that such states need not be jointly accessible. It is less clear that these cases also show that such states need not be jointly experienced. Michael Tye (2004) argues split-brain cases do have that implication, and Timothy Bayne and David Chalmers (2003) argue that they do not. I will develop two objections to Tye’s arguments. First, an analogy to blindsight on which he relies is questionable. (...) Second, even if his analogy succeeds, it shows only that a single person can simultaneously have two separate sets of phenomenally conscious mental states. That result fails to undermine the phenomenalunity thesis that Bayne and Chalmers defend, on which phenomenal consciousness is necessarily unified. (shrink)

The phenomenon of multiple personality--Like the "split-Brain" phenomenon--Involves a disintegration of the normally unified self to the point where one must question whether there is one, Or more than one, Person associated with the body even at a single moment in time. Besides the traditional problem of determining identity over time, There is now a new problem of personal identity--Determining identity at a single moment in time. We need the conceptual apparatus to talk about this new problem and a test, (...) Like the one I propose, For determining the number of persons associated with a body at a single moment in time. (shrink)

This paper challenges the widely held theory that split-brain patients have ‘two-minds’ and can thus be described as being two distinct persons. A distinction is made between the singularity of mind and the coherence of mind. It is stressed that ‘a single mind’ is not something posited to explain coherence among mental contents, but is merely a mark that such coherence holds to a certain degree. However, there is no sharp dividing line regarding what counts as a single mind. It (...) is argued that mental coherence is always a matter of degree, and that our concept of a single mind can accomodate spit-brain phenomena. (shrink)

How should we count people who have two cerebral hemispheres that cooperate to support one mental life at the level required for personhood even though each hemisphere can be disconnected from the other and support its "own" divergent mental life at that level? On the standard method of counting people, there is only one person sitting in your chair and thinking your thoughts even if you have two cerebral hemispheres of this kind. Is this method accurate? In this paper, I (...) argue that it is not, and I advocate an alternative I call the Multiple Person View. (shrink)

The article questions the assumption that conjoined twins are necessarily two people or persons by employing arguments based on different points of view: non-personal vitalism, the person as a sentient being, the person as an agent, the person as a locus of narrative and valuation, and the person as an embodied mind. Analogies employed from the cases of amputation, multiple personality disorder, abortion, split-brain patients and cloning. The article further questions the assumption that a conjoined twin's natural interest and wish (...) is separation. I first contend that separation is such a radical procedure as to render the post-separation person different from the pre-separation one. Therefore, it is not possible to benefit the pre-separation twin by the act of separation. The article concludes with a critical evaluation of the tendency in bioethics to regard ethical challenges as rivalry between individuals competing for scarce resources. (shrink)

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)

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.

Thought-experiments in which one person divides into two have been important in the literature on personal identity. I consider three influential arguments which aim to undermine the force of these thought-experiments – arguments from David Wiggins, Patricia Kitcher and Kathleen Wilkes. I argue that all three fail, leaving us to face the consequences of splitting, whatever those may be.

Thought-experiments in which one person divides into two have been important in the literature on personal identity. I consider three influential arguments which aim to undermine the force of these thought-experiments – arguments from David Wiggins, Patricia Kitcher and Kathleen Wilkes. I argue that all three fail, leaving us to face the consequences of splitting, whatever those may be.

Derek Parfit's “reductionist” account of personal identity (including the rejection of anything like a soul) is coupled with the rejection of a commonsensical intuition of essential self-unity, as in his defense of the counter-intuitive claim that “identity does not matter.” His argument for this claim is based on reflection on the possibility of personal fission. To the contrary, Simon Blackburn claims that the “unity reaction” to fission has an absolute grip on practical reasoning. Now David Lewis denied Parfit's claim that (...) reductionism contravenes common sense, so I revisit the debate between Parfit and Lewis, showing why Parfit wins it. Is reductionism about persons then inherently at odds with the unity reaction? Not necessarily; David Velleman presents a reductionist theory according to which fission does not conflict with the unity reaction. Nonetheless, relying on the distinction between person level descriptions of first-person states and the first-person perspective itself, I argue that Velleman's theory does not eliminate fission-based conflict with the unity reaction. Footnotesa * Earlier versions of this paper were presented at the philosophy departments at Rutgers University and Bowling Green State University. I am indebted to many members of these audiences, and to the other contributors to this volume, for their comments—especially Frank Arntzenius, Michael Bradie, David Copp, John Finnis, Jerry Fodor, Brian Loar, Barry Loewer, Colin McGinn, Fred Miller, Mark Moyer, David Oderberg, Marya Schechtman, David Schmidtz, David Sobel, and Sara Worley. Special thanks to David Sanford. I am also grateful to graduate students in my seminar at Bowling Green during the spring of 2003, for urging me to take seriously the grip of the unity reaction; I am especially grateful for the comments of Nico Maloberti, Jonathan Miller, John Milliken, Robyn Peabody, Jennifer Sproul, Jessica Teaman, and Sherisse Webb. (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)

In this introduction to the special issue of Theoretical Medicine and Bioethics on the topic of personal identity and bioethics, I provide a background for the topic and then discuss the contributions in the special issue by Eric Olson, Marya Schechtman, Tim Campbell and Jeff McMahan, James Delaney and David Hershenov, and David DeGrazia.

ABSTRACT: We begin by discussing some logical constraints on the psychological approach to personal identity. We consider a problem for the psychological approach that arises in fission cases. The problem engenders the need for a non-branching clause in a psychological account of the co-personality relation. We look at some difficulties in formulating such a clause. We end by rejecting a recently proposed formulation of non-branching. Our criticism of the formulation raises some interesting questions about the individuation of person stages.RÉSUMÉ: Ce (...) travail traite d'abord de certaines contraintes logiques concernant l'usage de l'approche psychologique pour définir l'identité personnelle. Nous y examinons un problème touchant l'approche psychologique dans les cas de fission. Ce problème exige l'intervention d'une clause qui nie tout recours au branchement dans l'examen de la relation de co-personnalité. Nous avons rencontré certaines difficultés dans la formulation d'une teile clause. Pour conclure, nous rejetons uneformulation récente du non-branchement. Notre objection à cette formulation soulève quelques questions intéressantes concernant l'individuation de stades temporels personnels. (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.

I consider, and rebut, the argument from "twinning" - that zygotes can't be considered human individuals as two or more such individuals could be (sometimes are) produced from one zygote.

Pummer : 43–77, 2014) ingeniously wraps together issues from the personal identity literature with issues from the literature on desert. However, I wish to take issue with the main conclusion that he draws, namely, that we need to rethink the following principle: Desert.: When people culpably do very wrong or bad acts, they deserve punishment in the following sense: at least other things being equal they ought to be made worse off, simply in virtue of the fact that they culpably (...) did wrong—even if they have repented, are now virtuous, and punishing them would benefit no one. :43–77, 2014: 43–44) Pummer offers an argument that is intended to show that this principle, along with widely-held views about personal identity, entails an inconsistent triad of propositions. I agree. But I think Pummer's argument attacks a straw man. I believe that no-one holds Desert, at least as it is stated, and that once the principle is stated correctly it is easy to see that no inconsistent triad follows from it. So, Desert does not need rethinking. It just needs to be stated correctly. (shrink)

The Kinds of Things strongly supports the commonsense belief that in normal human life even changes in our deeply-held affections and ideals do not erode the ...

If we are physical things with parts, then accounts of what we are and accounts of when composition occurs have important implications for one another. Defenders of restricted composition tend to endorse a sparse ontology in taking an eliminativist stance toward composite objects that are not organisms, while claiming that we are organisms. However, these arguments do not entail that we are organisms, for they rely on the premise that we are organisms. Thus, sparsist reasoning need not be paired with (...) animalism, but could instead be paired with other accounts according to which we are composites. The embodied mind account—a version of the brain view—is one such account. Replacing the premise that we are organisms with the premise that we are embodied minds, in arguments that otherwise parallel those supporting animalist sparsism, yields an account according to which composite objects include thinkers, but perhaps nothing else. Since animalism has implausible implications about scenarios which are handled better by the embodied mind account, this approach is preferable to animalist sparsism. Furthermore, the role of mental features in sparsism makes embodied mind sparsism the more reasonable conclusion. Meanwhile, adopting sparsism allows the embodied mind account to dodge objections that may not be as easily avoided by it or other versions of the brain view if not paired with sparsism. These include objections about brains that are not persons, inorganic part replacement, and another form of part replacement that might seem to allow one to get a new brain. (shrink)

Memory theories of personal identity are subject to the difficulty that distinct simultaneous person stages may both stand in the memory relation to an earlier person stage. Apparently, Such theories entail that these two duplicate person stages are stages of the same person, A claim argued to be "obviously false". In this paper, I argue that the characteristics of these duplication cases usually cited to support this claim do not provide adequate evidence to make it cogent.

In attempting to understand personal identity, it is common practice to imagine a person existing at some time t and a person existing at a time t* , and then to ask, What does it take for person x at t to be the same person as person y at t*?The Psychological Continuity Approach answers: there is a relation, R, of psychological continuity such that person x at t is the same person as person y at t* if and only (...) if x at t bears R to y at t*.But maybe the question above is not the right one to ask when trying to understand personal identity. Olson calls this the narrow question of personal identity, which he distinguishes from the broad question: What does it take for person x at t to be the same individual as y at t*? (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)

In this discussion paper, I evaluate some arguments of Mark Johnston's which appear in his articles «Fission and the Facts» and «Reasons and Reductionism» . My primary concern is with his description of fission cases, and his assessment of the implications of such cases for value theory. In particular, Johnston advances the following three claims:Rejecting the intrinsicness of identity is an arbitrary response to the paradox of fission;Fission cases involve indeterminate identity;Contra Parfit, fission cases have no implications for value theory (...) in the actual world.I argue that and are false, and that , if true, is not true for any reason that Johnston gives. (shrink)

Through careful analysis of a specific example, Parfit’s ‘fission argument’ for the unimportance of personal identity, I argue that our judgements concerning imaginary scenarios are likely to be unreliable when the scenarios involve disruptions of certain contingent correlations. Parfit’s argument depends on our hypothesizing away a number of facts which play a central role in our understanding and employment of the very concept under investigation; as a result, it fails to establish what Parfit claims, namely, that identity is not what (...) matters. I argue that Parfit’s conclusion can be blocked without denying that he has presented an imaginary case where prudential concern would be rational in the absence of identity. My analysis depends on the recognition that the features that explain or justify a relation may be distinct from the features that underpin it as necessary conditions. (shrink)

It has been argued that 'brain bisection' data leads us to abandon our traditional conception of personal identity. Nagel has remarked: The ultimate account of the unity of what we call a single mind consists of an enumeration of the types of functional integration that typify it. We know that these can be eroded in different ways and to different degrees. The belief that even in their complete version they can be explained by the presence of a numerically single subject (...) is an i1lusion.l Parfit has adopted a similar position, contending that patients with 'split brains' become two separate 'streams of consciousness' and thus that our normal sense of personal identity, or at least 'what matters' about personal identity is constituted by psychological relations between connected conscious experiences2 It is claimed that in 'split brain' patients certain of the relations are disrupted and that we thus see clearly that the nature of the unity that is normally present does not reside in a single subject with a given identity, but in the connectedness and continuity that normally obtains. Parfit draws on two sources of support for these contentions: the first is the actual events that transpire after a human being is submitted to the operation of sectioning the corpus callosum (or 'brain bisection'), and the second is the imaginative consideration of various scenarios involving graded mental and physical discontinuity, and the 'fission' and 'fusion' of persons. I shall do little more than argue that the actual data will not sustain the interpretation put on them. (shrink)

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)

In this paper it is argued that the experimental data on commissurotomy patients provide no grounds for denying the singular personhood of commissurotomy patients. This is because, contrary to most philosophical accounts, there is no “unity of consciousness” discriminating condition for singular personhood that is violated in the case of commissurotomy patients, and because no contradictions arise when singular personhood is ascribed to commissurotomy patients.

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.

Closest-continuer or best-candidate accounts of persistence seem deeply unsatisfactory, but it’s hard to say why. The standard criticism is that such accounts violate the ‘only a and b’ rule, but this criticism merely highlights a feature of the accounts without explaining why the feature is unacceptable. Another concern is that such accounts violate some principle about the supervenience of persistence facts upon local or intrinsic facts. But, again, we do not seem to have an independent justification for this supervenience claim. (...) Instead, I argue that closest continuer accounts are committed to unexplained correlations between distinct existences, and that this is their fundamental flaw. We can have independent justification for rejecting such correlations, but what the justification is depends upon much broader issues in ontology. There is no one-size-fits all objection to closest-continuer accounts of persistence. (shrink)

Hylomorphism offers a third way between animalist approaches to personal identity, which maintain that psychology is irrelevant to our persistence, andneo-Lockean accounts, which deny that humans are animals. This paper provides a Thomistic account that explains the intuitive responses to thought experiments involving brain transplants and the transformation of organic bodies into inorganic ones. This account does not have to follow the animalist in abandoning the claim that it is our identity which matters in survival, or countenance the puzzles of (...) spatially coincident entities that plague the neo-Lockean. The key is to understand the human being as only contingently an animal. This approach to our animality is one that Catholics have additional reason to hold given certain views about purgatory, our uniqueness as free and rational creatures, and our having once existed as zygotes. (shrink)

The neural substrates of context effects in word perception are still largely unclear. Interhemispheric priming phenomena in word recognition, typically observed in normal subjects, are absent in commissurotomized patients. This suggests that callosal fibers may provide contextual integration. In addition, certain characteristics of human frontal cortical fields subserving sensorimotor learning, as investigated by positron emission tomography, provide evidence for contextual integration not confined to the visual system. This supports the notion of common aspects of cortical computations in different cerebral areas.

Derek Parfit famously defends a number of surprising views about "fission." One is that, in such a scenario, it is indeterminate whether I have survived or not. Another is that the fission case shows that it does not matter, in itself, whether I survive or not. Most critics of the first view contend that fission makes me cease to exist. Most opponents of the second view contend that fission does not preserve everything that matters in ordinary survival. In this paper (...) I shall provide a critique that does not rely on either of these contentions. There are other, interrelated reasons to reject Parfit's defense of the two theses. In particular, the availability of the following view creates trouble for Parfit: I determinately survive fission, but it is indeterminate which fission product I am. (shrink)

Most versions of the psychological-continuity approach to personal identity (PCA) contain a 'non-branching' requirement. Recently, Robert Francescotti has argued that while such versions of PCA handle Parfit's standard fission case well, they deliver the wrong result in the case of an intact human brain. To solve this problem, he says, PCA-adherents need to add a clause that runs contrary to the spirit of their theory. In this response, I argue that Francescotti's counterexample fails. As a result, the revision he suggests (...) is not needed. (shrink)