Hardcastle supports my claim that Dennett's criterion for conscious selfhood -- having a robust narrative center of gravity --is counterintuitively narrow. Revonsuo provides strong empirical evidence in favor of this same view. Leiber suggests that my defence of right-hemisphere self-consciousness depends upon my accepting mind-brain identity theory, but this is incorrect. Mortensen et al. think I need their notion of "part-persons" to describe the disconnected cerebral hemispheres: I find it simpler to extend the notion of "person" to the nonspeaking hemisphere, yielding two persons per split-brain patient. Pessin's main critical reaction rests on a confusion about Dennett's "Multiple Drafts" theory of the mind.
2. Leiber's commentary (1993) puzzles me. On the one hand, his tone gives the impression that we are in profound disagreement, yet I agree with all the factual assertions he makes. How can we both agree and disagree? At the end, however, he writes that if I find Dennett's criterion of selfhood too narrow to accommodate an elderly left hemispherectomy case, this is because "granny is not simply a right hemisphere" (par. 3). But nowhere did I say she was. I have always rejected the Identity Theory as overly simplistic. (It is difficult enough to defend statements I actually have made!)
3. The commentary by Revonsuo (1993) provides powerful empirical support for my criticisms of Dennett, especially from studies of prosopagnosia (par. 3), where in brain-damaged patients there is disassociation between explicit and implicit facial recognition; patients deny recognizing the face but their information processing system gives covert evidence that the face is indeed a familiar one. And in the split-brain patients, information processing in the right hemisphere is just as oblivious to the dominant hemisphere; this is why my earlier theory of double consciousness in the normal, intact human brain (Puccetti, 1973) may turn out to be correct (par. 7).
4. Mortensen et al. (1993) get off to a shaky start in their commentary by observing that if I allow Dennett's claim that in experimental situations the disconnected right hemisphere of split-brain patients can support a transitory self, then I should allow for a full-fledged self following hemispherectomy (par. 2). But in fact behavioral evidence for consciousness, after removal of the self/speaking- hemisphere, is one of the reasons I denied that consciousness in the right hemisphere is only transitory. Nor is it clear to me how the absence of a left hemisphere itself provokes the elaboration of a "permanent self" in the residual right hemisphere. Is it not simpler to suppose that this nonverbal self-concept existed presurgically as well as postsurgically? But these commentators quickly move on to introduce their concept of a "part-person" (par. 3), which is what each of the two disconnected hemispheres becomes following cerebral commissurotomy: the right hemisphere because by itself it lacks linguistic thinking; the left hemisphere because it lacks spatial reasoning. So post- commissurotomy the survivor is not a person, but "two part-persons." Similar moves can be made, though with difficulty, with notions of "personality" (par. 4), "consciousness" (par. 5), and even "mind" and "self" (par. 3). My reply to all of this will be quite brief: we don't need to legislate language; we merely have to extend the concept of a person the nonspeaking cerebral hemisphere.
5. Pessin's commentary (1993) begins with the denial that Dennett's concept of consciousness as consisting of "Multiple Drafts" really conflicts with my own claim that split-brain surgery reveals the potential duality of mind in the normal, intact human brain (par. 1). He writes that Dennett's theory, like any "Society of Minds" view, conceives of mental activity as existing along a slippery slope from one mind to indefinitely many (par. 2) per human being, which would include the number two. Dennett, after all, concedes the "logical possibility" of there being a right hemisphere self. This is true, but the quote provided in par. 15 of the target article clearly denies that there is such a thing. Pessin's final word on this subject is that Dennett takes higher mental activity to be based in those very countable hemispheres (par. 3), but he adds, cryptically: "It's just that that needn't entail their own countability." At this point I am lost: how can the cerebral hemispheres be both countable and not countable? I think Pessin meant that although based in the two cerebral hemispheres, the mind's Multiple Drafts are not themselves countable, because the mind is only an abstraction. Which is what I said. In par. 8 Pessin defends Dennett's view by reducing it to innocuous statements about not going beyond the evidence in split-brain testing situations. But we should remind ourselves that we normals cannot give bifurcated responses in the same testing circumstances, which surely warrants the interpretation that our brains and theirs are informationally distinct (postsurgically) and not just during lab testing of the latter. In par. 9 and 10 Pessin parodies my criticisms.
6. Let me try to counter Pessin's moves by introducing a fresh observation. Suppose that, like 92% of us, you are right-handed. You fall and break your right arm. If you were a classroom teacher who had to write on the blackboard often, you could do so using your left arm (though clumsily). But now you incur a basilar stroke that effectively transects the corpus callosum, just as cerebral commissurotomy would. That means you are transiently agraphic; you can't write on the blackboard with either hand until your right arm is healed. But even so, you would never be able to write on the blackboard again using your left hand and arm, though before the stroke you were able to do so. What explains this outcome? I think the answer is that the left- arm/right-hemisphere combination can be viewed as a psychological system which, unlike the right-arm/left-hemisphere combination, does not have a learning history that includes writing. Before the stroke, your left (dominant) hemisphere was able to recruit homologous tissue from the right (nondominant) hemisphere to write with the left arm on the blackboard. Post traumatically, the stroke's effect was to block this option and render you permanently agraphic with that left arm. The testability of this claim is limited; I will say only that if I am right, firm split-brained right handers should prove to be incapable of writing sinistrally (I give a fuller treatment of this in Puccetti, in press.) In his conclusion (par. 12), Pessin says my recurring mistake has been to fail to distinguish between having a mind (or mental activity) and having a self. But is that a mistake? Ask yourselves: can there be a selfless human adult mind; or a mindless adult human self? I think not. These concepts, while not the same, are totally congruent.
Dennett, D.C. (1991) Consciousness Explained. Boston: Little, Brown.
Hardcastle, V.G. (1993) A New Agenda for Studying Consciousness. PSYCOLOQUY 4(57) split-brain.2.hardcastle.
Leiber, J. (1993) Conscience and Commissurotomy. PSYCOLOQUY 4(58) split-brain.3.leiber.
Mortensen, C., O'Brien, G & Paterson, B. (1993) Distinctions: Subpersonal and Subconscious. PSYCOLOQUY 4(62) split-brain.5.mortensen.
Pessin, A. (1993) One Mind Too Many? PSYCOLOQUY 4(64) split-brain.6.pessin.
Puccetti, R. (in press) Mind with a Double Brain. The British Journal for the Philosophy of Science.
Puccetti, R. (1993) Dennett on the Split-Brain. PSYCOLOQUY 4(52) split-brain.1.puccetti.
Puccetti, R. (1973) Brain Bisection and Personal Identity. British Journal for the Philosophy of Science 24: 339-55.
Revonsuo, A. (1993) Dennett and Dissociations of Consciousness. PSYCOLOQUY 4(59) split-brain.4.revonsuo.