An examination of split-brain syndrome, and whether split-brain patients have two minds.

Commissurotomy surgery has lately attracted considerable philosophical attention. It has seemed to some that the surgical scalpel that bisects the brain bisects consciousness and the mind as well; and that the ordinary concept of a person is thereby most seriously threatened. I shall assess the extent of the threat, arguing that it is overestimated. The argument begins with section III; section II, which describes the operation and its effects, should be omitted by those already familiar with these facts.

This concise monograph argues that experiments on patients who have had radical commissurotomies disconnecting their right and left cerebral hemispheres do not show that such patients, or nonpatients in general, are not unified persons. For Marks "the split-brain patient has one mind and is one person, although he has on occasion, a disunified consciousness. The experimental results pose no special threat to our concept of the unity of a person". Marks's position relies on three sources: the Wittgensteinian view that philosophical (...) problems are often created by philosophers' seduction by inept metaphors where careful attention to language is needed; the functionalist view that the mind just is that which the most satisfactory scientific explanation of human behavior postulates; and a burden-of-proof attack against his opponent. (shrink)

Commissurotomy surgery has lately attracted considerable philosophical attention. It has seemed to some that the surgical scalpel that bisects the brain bisects consciousness and the mind as well; and that the ordinary concept of a person is thereby most seriously threatened. I shall assess the extent of the threat, arguing that it is overestimated. The argument begins with section III; section II, which describes the operation and its effects, should be omitted by those already familiar with these facts.

If a conception like the commissural-integrative conception of the normal stream of consciousness is correct, then we should expect to find that the consciousness of the deconnected left hemisphere is not a normal consciousness, because the right hemisphere cannot contribute to the left hemisphere's stream except by means of inadequate subcortical connections. Therefore, the present article considers, from the literature, three hypothesized dimensions of deconnected left-hemispheric consciousness: Is the deconnected left hemisphere alienated as agent from behavior produced by the respective (...) right hemisphere? Or does the deconnected left hemisphere appropriate the latter behavior to the person, as it does behavior that the left hemisphere itself produces? Is the stream of consciousness of the deconnected left hemisphere more narrow and more disunified than the normal stream? Or is the left hemisphere's total state of consciousness of the moment just as rich as the normal stream, both in the part-experiences that comprise it and in awareness of relations among these part-experiences? Is the deconnected left hemisphere unaware of the commissurotomy-produced deficiencies characterizing its stream of consciousness? Or does the deconnected left hemisphere have awareness of what it, taking itself to be the whole person, can no longer accomplish? Discussion of these questions should go forward; they represent natural directions in which to investigate what is distinctive about left-hemispheric consciousness-which, the commissural-integrative view holds, has been produced by surgery. (shrink)

If a conception like the commissural-integrative conception of the normal stream of consciousness is correct, then we should expect to find that the consciousness of the deconnected left hemisphere is not a normal consciousness, because the right hemisphere cannot contribute to the left hemisphere's stream except by means of inadequate subcortical connections. Therefore, the present article considers, from the literature, three hypothesized dimensions of deconnected left-hemispheric consciousness: Is the deconnected left hemisphere alienated as agent from behavior produced by the respective (...) right hemisphere? Or does the deconnected left hemisphere appropriate the latter behavior to the person, as it does behavior that the left hemisphere itself produces? Is the stream of consciousness of the deconnected left hemisphere more narrow and more disunified than the normal stream? Or is the left hemisphere's total state of consciousness of the moment just as rich as the normal stream, both in the part-experiences that comprise it and in awareness of relations among these part-experiences? Is the deconnected left hemisphere unaware of the commissurotomy-produced deficiencies characterizing its stream of consciousness? Or does the deconnected left hemisphere have awareness of what it, taking itself to be the whole person, can no longer accomplish? Discussion of these questions should go forward; they represent natural directions in which to investigate what is distinctive about left-hemispheric consciousness-which, the commissural-integrative view holds, has been produced by surgery. (shrink)

This is the third in a series of articles that address what is known or knowledgeably held about the consciousness of fully commissurotomized people. This installment discusses three alternative conceptions with which the present author does not agree. They are Eccles's dualist-interactionist conception, Gillett's linguistic conception, and Rey's eliminative conception. With regard to the first two of these, issues are raised with the intention of helping the respective proponent to improve his conception. In the case of the third, it is (...) urged that the view not be promoted, for moral reasons, unless very strong evidence sometimes becomes available in its favor. (shrink)

This article addresses the problem of evidence for Puccetti's hypothesis of normal dual consciousness, i.e., the hypothesis that a stream of consciousness flows in each cerebral hemisphere when both are functioning normally in intact, healthy people. Evidence counts as supportive only if it is not explainable by a certain close alternative hypothesis that holds consciousness to proceed in the nondominant hemisphere only when the dominant hemisphere is unable to inhibit it . From this perspective, I discuss two experiments involving anesthesia (...) of the dominant hemisphere that were proposed, respectively, by Wilson and Puccetti, an actual experiment on normal, unanesthetized subjects reported by Landis, Graves, and Goodglass, as well as a further kind of experiment which, I suggest, may discriminate between the hypotheses. Assuming Puccetti is right, this experiment should yield a distinct pattern of reports from the dominant hemisphere about its experiences of acting as the individual deals with different kinds of tasks . Also considered is the common introspective evidence to the effect that we have only a single stream, never two distinct experiences at the same time. I argue, in support of Puccetti, that this is as it should be because introspection-at-a-distance is impossible; privileged access is internal to a stream, never occurs between streams. (shrink)

Hurley’s is a difficult book to work through—partly because of its length and the complexity of its arguments, but also because each of the ten essays of which it is composed has a rather different starting point and focus, and because few of her arguments achieve real closure. Essay 2 discusses competing interpretations of Kant, essay 4 articulates nonconceptual forms of self-consciousness, essay 5 offers fresh interpretations of commissurotomy patients’ behavior, essay 6 develops an objection to Wittgenstein on rule following, (...) essay 8 attacks an alleged assumption of externalism, and chapter 10 explores the possibility of combining a “motor theory” and a “control theory” of perception. This is a very rich brew, and at least half the challenge this book presents consists in discerning its central argument and conclusion with enough precision to bring criticism to bear. (shrink)

To assess the ability of the disconnected cerebral hemispheres to recognize images of the self, a split-brain patient was tested using morphed self-face images presented to one visual hemifield at a time while making “self/other” judgments. The performance of the right and left hemispheres of this patient as assessed by a signal detection method was not significantly different, though a measure of bias did reveal hemispheric differences. The right and left hemispheres of this patient independently and equally possessed the ability (...) to self-recognize, but only the right hemisphere could successfully recognize familiar others. This supports a modular concept of self-recognition and other-recognition, separately present in each cerebral hemisphere. (shrink)

What are you and I essentially? When do you and I come into and go out of existence? A common response is that we are essentially organisms, that is, we come into existence as organisms and go out of existence when we cease to be organisms. Jeff McMahan has put forward two arguments against the Organism View: the case of dicephalus and a special case of hemispheric commissurotomy. In this paper, I defend the Organism View against these two cases. Because (...) it is possible to devise more McMahanian-type cases, I also provide a more general solution to these kinds of cases. (shrink)

Over the past several years, the study of self-related cognition has garnered increasing interest amongst psychologists and cognitive neuroscientists. Concomitantly, lesion and neuroimaging studies have demonstrated the importance of intact cortico-cortical and cortico-subcortical connections for supporting high-level cognitive functions. Commissurotomy or “split-brain” patients provide unique insights into the role of the cerebral commissures in maintaining an individual’s sense of self, as well as into the unique self-representation capabilities of each cerebral hemisphere. Here we review empirical work examining the integrity of (...) self-related processes in patients with various disconnection syndromes, focusing on studies of self-recognition, ownership, and agency. Taken together, this body of work suggests that an intact corpus callosum enabling interhemispheric transfer is necessary for some, but not all types of self-representations. (shrink)

In this commentary I use recent empirical evidence and theoretical analyses concerning the importance of language and the meaning of self-recognition to reevaluate the claim that the right mute hemisphere in commissurotomized patients possesses a full consciousness. Preliminary data indicate that inner speech is deeply linked to self-awareness; also, four hypotheses concerning the crucial role inner speech plays in self-focus are presented. The legitimacy of self-recognition as a strong operationalization of self-awareness in the right hemisphere is also questioned on the (...) basis that it might rather tap a preexisting body awareness having little to do with an access to mental events. I conclude with the formulation of an alternative interpretation of commissurotomy according to self-awareness — a “complete” one in the left hemisphere and a “primitive” one in the right hemisphere. (shrink)

Jeff McMahan has recently developed the embodied mind theory of identity in place of the other standing theories, which he examines and consequently rejects. This paper examines the performance of his theory on cases of commissurotomy or the split-brain syndrome. Available experimental data concerning these cases seem to suggest that a single mind can divide into two independent streams in ways that are incompatible with our intuitive notion of mind. This phenomenon poses unique problems for McMahan's theory that we are (...) essentially minds. I attempt to use his considered response to these cases as a weapon against his own embodied mind theory by highlighting some of the tensions in McMahan's response. In particular, I argue that in reaching his conclusion McMahan admits to something quite contrary to the very spirit of his own theory and that it is a powerful point in its support that one of the theories McMahan rejects can deal very well with these cases. (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)

Hurley’s is a difficult book to work through—partly because of its length and the complexity of its arguments, but also because each of the ten essays of which it is composed has a rather different starting point and focus, and because few of her arguments achieve real closure. Essay 2 discusses competing interpretations of Kant, essay 4 articulates nonconceptual forms of self-consciousness, essay 5 offers fresh interpretations of commissurotomy patients’ behavior, essay 6 develops an objection to Wittgenstein on rule following, (...) essay 8 attacks an alleged assumption of externalism, and chapter 10 explores the possibility of combining a “motor theory” and a “control theory” of perception. This is a very rich brew, and at least half the challenge this book presents consists in discerning its central argument and conclusion with enough precision to bring criticism to bear. (shrink)

The purpose of this article is to explore the possibility that studies in cerebral commissurotomy (severing of the corpus callosum) may shed some light on Jean-Paul Sartre's account of bad faith. I shall examine this issue from both a descriptive and an explanatory point of view. My conclusion will be that Sartre and various neuroscientists seem generally to agree on the description of self-deception, but they substantially disagree on how the phenomenon is to be explained. I shall argue that Sartre's (...) account does not seem fully adequate, while the neuroscientific approach may have explanatory potential if certain conceptual issues are resolved. I shall also argue that, carefully delimited, the neuroscientific .. (shrink)

This is the third of four online Companions to Velmans, M. (ed.) (2018) Consciousness (Critical Concepts in Psychology), a 4-volume collection of Major Works on Consciousness commissioned by Routledge, London. -/- The Companion to Volume 3 introduces major phases and findings in the search for the neural correlates of consciousness (NCC) starting with the time it takes for these to form and the wider research program that might lead to their discovery. This includes the search for mechanisms responsible for “neural (...) binding”—how widely dispersed neural activities support integrated conscious experiences, and the search for neural markers of consciousness that can serve to distinguish conscious from preconscious and unconscious activities in the brain. We then turn to global disorders of consciousness that indirectly reveal the conditions that support consciousness by establishing what abolishes it or impairs it, and conclude this section with reviews of the major challenges in the search for NCCs that still remain. This survey then continues with research on the divided brain with cerebral commissurotomy patients, which proved to be very useful in determining the respective functions of the left and right halves of the brain. It also raised philosophical questions. Could consciousness itself be divided by this operation? And, if so, would such patients have a distinct left-brain and right-brain consciousness? Philosophical issues also combine with methodological and experimental developments in the following sections on the reintroduction of first-person methods and how to combine these with complementary, third-person methods in neurophenomenology and experiential neuroscience—two well-developed research programs for both investigating consciousness and understanding its functions. This Companion (and associated Volume) then concludes with a survey of research on free will, covering both the major findings arising from neuropsychological research and a way to understand these that is consistent with a natural understanding of volition, ethics, and legal responsibility. -/- As with the other Companions to these Volumes there are many links to background resources (marked in pink) and to the selected readings themselves (marked in blue). -/- . (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.

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.

In _Consciousness and persons_, Michael Tye. Consciousness and persons. Cambridge, MA: MIT Press.) develops and defends a novel approach to the unity of consciousness. Rather than thinking of the unity of consciousness as involving phenomenal relations between distinct experiences, as standard accounts do, Tye argues that we should regard the unity of consciousness as involving relations between the contents of consciousness. Having developed an account of what it is for consciousness to be unified, Tye goes on to apply his account (...) of the unity of consciousness to the split-brain syndrome. I provide a critical evaluation of Tye's account of the unity of consciousness and the split-brain syndrome. (shrink)