It is sometimes claimed that personalist Neo-Cartesian Dualism as a serious philosophical candidate within the mind-body debate may be declared 'dead'. (See for example this paper by Keith Augustine.)
The experimental and clinical findings of neuropsychology would unequivocally show that the brain is the sole cause and source of consciousness and cognition. However, the only thing that these findings really show is that the mind may to a large extent be influenced
by the brain. In fact, this insight is not only compatible with Neo-Cartesian Dualism, it is an intrinsic aspect of this theory!
Anti-dualists seem very fond of confusing the predicate "being influenced by" with "being existentially dependent on". If they were right, the very same would have to hold for the brain. As I showed elsewhere,
from a logical point of view the brain simply must be influenced by consciousness (subjectivity), unless we wish to believe that consciousness does not exist. So if influence really equals dependence, this would suggest that the brain is dependent on consciousness for its
very existence. However, - outside the peculiar Buddhist theory of complete interdependence - they obviousy cannot both be equally dependent on each other for their existence. In other words, influence does not equal dependence!
There is one subfield of neurology that seems less obviously irrelevant: experiments with split-brain patients which at first sight may appear to show that within an experimental context they possess two separate streams of consciousness. (A related phenomenon may be the so called alien hand syndrome.) If this
interpretation were the only one possible, substance dualism would be in serious trouble (it would certainly not discredit personalist dualism in general by the way, as it might be reconciled with emergent semi-substantialist dualism as defended by Karl Popper). However, there
is a lot of debate about this issue, and there is no general consensus that the data should inevitably be explained in this manner. As John Beloff (whose dualism might be less personalist than mine) remarked in a paper about dualism, during these experiments one of the apparently conscious
streams of consciousness may simply be subconscious (i.e. mentally active, but at a non-conscious level). The phenomenon would presumably be caused by the peculiar experimental setting which makes the simultaneous conscious integration of all the data into one total picture impossible. The fact that subconscious processing is allowed to express itself through one of the hands may be due to the experimental setting as well, or else it might be related to a lower level of inhibitory control (caused by commissurectomy) by consciousness of motoric expressions based on mental, non-conscious processing (perhaps
functionally comparable to the strange exclamations of patients suffering from the Gilles de la Tourette-syndrome, expressions which may be humorous and to the point but which are not usually seen as based on conscious thought either). The personal self would consciously be aware of only one part of the perceptual data and the rest of the information would reach its subconscious mind. The process would be comparable to other settings such as subliminal perception, blindsight and automatic writing, in that there would be a lot of parallel cognitive processing going on, but exclusively at a subconscious (or non-conscious) level rather than by (or through) a
presumed co-consciousness. As we can also see in those other cases, this type of processing may be a lot more complex and intentional than what we would expect of a 'blind', mindless automaton, but there is no reason to suppose that it also has to be conscious (in the sense of subjectively experienced by a subject). It is certainly wrong to suppose that subjectivity has absolutely no impact on the brain (as is claimed in epiphenomenalism
and other forms of physicalism) but it is also wrong to believe that all 'creative' cognitive processing and responses must inevitably be caused by consciousness, unless we wish to confuse two very different
meanings of the word conscious, i.e. (cognitively, but not necessarily subjectively) aware and subjectively experienced (in other words: specifically subjectively aware). We
know from psychological and psychiatric literature that people may develop subconscious personality structures and it is enough to conclude that part of the perceptual information presented in split-brain experiments cannot reach consciousness though it is still processed and acted upon on a subconscious level, by a subconscious part of the person's personality. So there would be no creation of a
new, separate mind or self (in the sense of conscious subject), but it would simply be another (rather limited) example of a cerebral impact on the mental activity of a substantial personal self, namely a limited impact on the integration of perceptual data in consciousness during
specific experiments. Results of split-brain experiments would remain special in other respects (e.g. regarding the localisation of parts of the brain that specifically interact with specific mental functions), but not in the sense that they would prove the supposed divisibility of
the self. The subsequent processing of the data that are not accessed consciously does not have to be influenced directly by the condition of split-brain. It is more parsimonious to assume that as the data are not (rather than separately) perceived consciously, their further cognitive elaboration, and any motor response following from this, is shielded from consciousness as well. This would also explain unexpected emotional responses and the release of repressed wishes, attitudes, styles of communication, etc. through the (part of
the) motor apparatus linked to the (non-dominant) hemisphere that is (during these experiments) not directly, interactively associated with consciousness. Similarly, data perceived consciously might not always be taken along during the subconscious processing of data shielded from
consciousness. In that sense, during the split-brain experiments there may be two (or more) chains of relatively independent parallel processing going on within the mental life as a whole of one and the same self. It may well be this temporary independence of the chains of processing that leads scholars to the conviction that there
are now two truly independent minds in one and the same skull. This mistake amounts to the confusion of functional dissociation within the self's mental life with ontological dissociation of the very self. Functional dissociation is compatible with substantialism.
We already know very similar phenomena from the field of automatic writing in persons who have not undergone a commisurectomy. Parts of these subconscious characteristics do not need to have been created by splitting the brain, but they may have been present a lot longer. We do
not have to embrace psychoanalytic theory to accept that a lot of our psychological structure normally does not reach the surface of consciousness. It
is rather amusing to see how some theorists think they can prove the presence of consciousness just by pointing to complex verbal responses or the manifestation of unusual attitudes. Both are rather thoroughly covered in the literature on subconscious processes. If these theorists
were right, there would be no philosophical problem of the presence of consciousness in others. This can only be true if the existence of complex or verbal subconscious processing is excluded a priori!
Again, epiphenomenalism and physicalism are very wrong, but that is not to say that we should ignore all the evidence for subconscious (or non-conscious) mental processing. By the way, the 'hunches' some subjects may have about data that are not consciously perceived, do not
have to be explained by the mysterious transmission of ideas through remaining nervous pathways, but it is sufficient to simply see them as messages from the subconscious mind which remains as much part of the
mental life of the self as before. Summing up, if one accepts the reality of subconscious mental processes, as is widely done in Neo-Cartesianism, there is nothing about split-brain experiments that would constitute a serious threat to personalist substantialist dualism. In fact, substantialist dualism even offers a plausible
explanation for the finding that most split-brain persons seem perfectly normal and integrated. They remain one and the same person, though some of their (own) mentation becomes (at least temporarily) inaccessible to consciousness.
If anyone seriously wishes to entertain the position that
split-brain does create two conscious minds, he or she should realise the following: - According to more than one author, the theory of two conscious minds seems incompatible with the over-all unity of mental functioning shown in split-brain patients outside the experimental (split-brain) setting. This unity would not be explainable
through the dominance of one hemisphere and it would include complex motor skills such as playing the piano that involve the active participation of both the cerebral hemispheres. As Wolfgang Gasser
formulates it nicely: "Cutting the lines of communication between the two sides of a brain (split brain patients) has incredibly few consequences. Primarily it is the soul which continues maintaining the coordination of the two sides." The unity of behavior after splitting the brain is even observed in non-human mammals, which in tragic
moral contradiction with the fact they are 'sacrificed' for research clearly suggests they are substantial selves just like humans. - There is no plausible theory that would explain the emergence of a non-physical conscious self out of non-conscious physical processing. In fact, it is not at all plausible that a persistent entity like the self, an entity known as a metaphysical substance,
could ever emerge from non-substantial physical phenomena (i.e. processes in the brain) which are by their very nature transient and ephimeral. Unless somebody shows why it is absolutely necessary (logically speaking) to believe in emergence, we should a priori avoid this theory. As we cannot have conclusive empirical evidence for the
existence of a co-consciousness, the interpretation of split-brain theory is primarily an ontological enterprise! In other words, anti-dualists are begging the question if they claim that split-brain experiments (rather) conclusively show that the conscious self emerges from the brain. Their conclusion simply amounts to the very ontological framework they start their intepretation from, coming full circle. (By the way, emergent substance dualism is actually held by William Hasker. In his contribution "Persons and The Unity of Consciousness" to The Waning of Materialism (Oxford, 2010, edited by Robert C. Koons and George Bealer) he states that explaining the results of experiments on split-brain patients by the creation of a co-consciousness through the somatogenic emergence of a new self is only natural. However, he seems to overlook the fact that the situation in such experiments is far from natural itself and that we cannot blindly rely on everyday intuitions in such cases, if reason seems to contradict them.)
Any valid argument against emergent materialism or emergent dualism within the philosophy of mind should automatically be seen as a valid argument against the emergentist interpretation of split-brain data in terms of creation of a new self as well. - In general, we already
know that there are complex non-conscious or subconscious cognitive processes and that they may have a strong impact on behavior. Therefore, it is more parsimonious to explain split-brain phenomena by such known processses than to prefer an exotic new theory of the creation of two conscious minds by the severing of the corpus callosum,
just for the sake of debunking radical substance dualism. - The hypothetical creation
of a conscious mind by splitting the brain would imply that the mind can most probably be destroyed as well by brain death. This would certainly be incompatible with what is suggested by important empirical data in the fields of Near-Death studies, reincarnation research in young children, etc. Such phenomena clearly seem to show that the personal mind is much more than just a product of the brain and that it can survive brain death.
Now, it is very unfair to ask from dualists that they adhere to an anti-dualist, dogmatic interpretation of split-brain data, while they are also expected to ignore anything that cannot be reconciled with such an interpretation. A good theory is supposed to explain all the available relevant data rather than to simply dismiss a large part of
them. (An original but implausible 'compromise' is suggested by Peter Novak, namely that there are already two substantial minds in the brain before commisurectomy and that both may actually survive death separately.)
Even if we accepted a non-substantialist interpretation in terms of the production of a new self by commisurectomy, this would not imply that a 'self' in the sense of subject could itself (rather than its mind) be divided into more selves. We would 'only' have to accept that
dividing the two hemispheres somehow creates a self. The self or experient (as such) should continue to be seen as indivisible, because how could one experient be literally divided into more than one experient! So the creation of a self should be a creation out of nothing (ex nihilo), as it is not created from the original self (there can be no Adam's rib in this context) nor from the stuff the brain is made of. This is
a very problematic concept which cannot possibly be associated with a material system such as the brain. So much for the debunking of the indivisibility-claim of substantialism.
The topic of split-brain is sometimes used in futuristic thought experiments involving the consequences for personal identity of brain transplants of one hemisphere. Usually, these experiments seem to start from materialist interpretations of split-brain data. It is possible that in the foreseeable future some of these experiments
may actually be carried out in practice. What would it imply if the severed hemispheres would survive separately and if they would apparently both be related to a separate personality? Strange as this may seem, such experiments would not prove anything either. First of all, we should not forget that unless we would ascribe spatial dimensions to the non-physical self, the link between a brain or
hemisphere and a non-physical self cannot be spatial in any literal sense. This means that the self may continue to interact with the two hemispheres, even if these are completely separated spatially (i.e. to a larger extent than by commisurectomy). As I said before, there can be
no full-proof empirical demonstration of the presence of consciousness linked to any physical system (except if we see our own introspection as such a demonstration in our own individual case). Thus, there can never be any type of experiment (compare: W.D. Hart, please scroll)
that would show that splitting the brain really implies creation of a new conscious self. It will for ever remain an ontological question and cannot be determined empirically.
Dualism is very much alive and kicking! Let's concentrate on making it (even) more sophisticated. I invite any theorist who would like to elaborate upon these remarks to contact me.
A false analogy
Some scholars might claim we can deduce from the behavior connected to the non-dominant hemisphere that it is accompanied by a separate stream of subjective consciousness and therefore by a separate experient. We
infer that others are conscious beings on the basis of their behavior and nervous system. We use an implicit analogy postulate, whereby it is also possible to infer that non-human animals undergo subjective experiences. Why should this be any different in the case of split-brain patients?
However, the analogy is false as we know for certain that the structure of the nervous system in such patients is different in a non-trivial way from that of the average brain with an intact corpus callosum.
It simply amounts to begging the question to believe that certain behaviors are always accompanied by subjective awareness, even under extreme conditions like a split brain.
A recent addition (October 2007) While responding to this paper, Mr. William (Bill) Loftus-Rooney recently made the following interesting observation:
I find it interesting that in discussions of split-brain patients, materialists rarely bring up Agenesis of the Corpus Callosum. People born with split-brains, while experiencing such things as retardation, autism, or lack of coordination, sometimes do not show these remotely, and NEVER show the supposed "two people". I see this as a proof against the "split-self" interpretation. [He pointed to] A[now expired] website [which] shows an overview of symptoms, none of which are "two selves" or "two consciousnesses". Also, interesting to note, the famous savant autistic Kim Peek had Callosum Agenesis.
I agree with Bill Rooney that such phenomena certainly do not confirm the split-self interpretation of experimental data relating to split-brain patients.