How does this computer analogy apply to the mind-brain problem? Let me give you a personal example: I am absolutely persuaded that my thoughts influence my brain’s activity. Why do I believe this? I have seen the EEG tracings from my own head, recorded in Donald MacKay’s laboratory, and they show dramatic changes as I voluntarily chose to think about different topics. To say that the physical, measurable changes in my brain’s activity were “determined” or “caused” by my thoughts does not require the existence of any particular organ of interaction through which my thoughts could “disturb” the normal pattern of my brain’s activity. On the other hand, I reject the notion that the thoughts I was thinking were merely my way of expressing, or giving a name to, the particular patterns of activity going on inside my brain at that moment. I reject that notion, because I had absolutely no conscious knowledge of the patterns of my brain’s activity until I saw the EEG tracings. The moment-by-moment changes in my brain’s activity, observable by the EEG technician, were completely unavailable to me, the owner of the brain, as part of my conscious experience at the time.
How would MacKay explain the correlation between my thoughts and my brain activity without resorting to interactionism or to emergentist materialism? Let me quote from his commentary (MacKay, 1978):
When I am thinking, doubtless my brain is engaged in physical activity whose form reflects what I am thinking, as the form of a computer’s internal activity reflects the equation it is solving; but the two levels in each case are conceptually distinct, their categories hierarchically complementary. (p. 600)
MacKay’s term for this is embodiment; our conscious thoughts are embodied in the physical brain processes that reflect the form of those thoughts. If the physical brain processes had a different form (as for example, if an area of my brain were stimulated electrically without my knowledge), my conscious thoughts would be different and the new thoughts would be embodied by the new pattern of brain activity.
This concept enabled MacKay to trace a path between interactionism and materialism. MacKay’s notion of embodiment allowed him to reject the dualistic two-world view of Popper and Eccles. For MacKay, there are no mental events without brain events, no thoughts without neural processes to embody them, and thus no need to speculate on a special way for the two worlds to interact. But MacKay’s notion of embodiment also allowed him to reject the rigid monism of Bunge. To quote MacKay:
We have seen that this does not mean that our mental activity is identical with the correlated brain activity, or a mere subclass of brain activity … Nor does this mean that the mental is “only an aspect” of the physical, as if the physical were somehow more real and fundamental. The two may perhaps be better described as complementary aspects of our unitary conscious agency. (1978,p. 605)
This brings us to MacKay’s third main point: the notion of embodiment does not diminish human responsibility. Contrary to Bunge’s claims, MacKay argued that brains (or their subsystems) do not think, or hope, or fear, or decide. It is people, acting as conscious agents, who do these things. It may well be that in a completely materialistic, mechanistic, deterministic system, human intentions and decisionmaking could be nothing more than illusions or by-products of physical brain activity, and thus humans could not be held accountable for their actions. But as MacKay pointed out, direct experience runs counter to this idea. He states (MacKay, 1978): “We know for a fact that we can make deliberate decisions and act upon them in the physical world.” (p. 600)
A few months after MacKay’s commentary appeared, Bunge published a rebuttal (Bunge, 1979) in which he restated his materialist views, claiming that “according to [the scientific world outlook] there are only concrete things” and that “the [components] of scientific theories are to be objective material entities, such as neurons, [not] subjective and allegedly immaterial ones, such as ideas” (p. 453). He also reiterated his claim that mental events were identical to brain events, stating, “For example, loudness or felt sound intensity, seems to be identical with the frequency of firing of certain neural subsystems of the auditory apparatus.” (p. 453) MacKay published a brief response (MacKay, 1979) in which he refused to yield any ground to Bunge’s attack. He states:
I argued that we have an adequate basis for mechanistic psychophysiological research if conscious agency is thought of as embodied in (rather than identical with) our cerebral processes, so that the activity of brain-and-body depends on mental activity in the intimate sense in which the form of a computer’s activity depends on the equation it is solving. To this claim Bunge fails to raise any cogent objection; and he nowhere shows that his postulated “identity” between mind and brain is scientifically necessary. (p. 454)
As for Bunge’s example of sound intensity, it was an unlucky choice, because one of MacKay’s research associates had just demonstrated that perceived loudness cannot be predicted solely on the basis of neural firing rate. MacKay continued:
Even if this were not so, however, the most that experiment could demonstrate is a correlation–not an identity–between perceptual experience and neural firing rate. (p. 454)
I take this as MacKay’s fourth main point, namely, that not only is an identity between mental events and brain events not scientifically necessary, it would be impossible to demonstrate such an identity.
Was MacKay successful in his attempt to trace a path between interactionism and materialism? I will leave that historical judgment to the current philosophers of science. I continue to have great respect for Bunge’s position, especially as he expanded it in his book entitled The mind-body problem: A psychobiological approach (Bunge, 1980). Yet I don’t believe that Bunge made an airtight case for psychoneural identity, and thus I see a continuing place for MacKay’s perspective. In fact, in a recent review of the neuroscience underlying mental disorders by Andreasen (1997), the mind-brain problem is described in terms that MacKay would have been comfortable with. The question is not yet settled; I believe that contemporary philosophers and psychologists can benefit from a continuing dialog on whether there is room to stand between interactionism and materialism. Those involved in such a dialog would do well to ponder MacKay’s last words from his response (MacKay, 1979):
I believe that the interactionist and the materialist are each seeking to conserve a real truth about our human nature. The materialist recognizes that our physical embodiment invites (and rewards) analysis in the same physical terms as the rest of the material world. The interactionist recognizes that the reality of what it is to be a conscious agent is richer–has more to it–than can be described in material (or, for that matter, in mental) terms alone. The argument of my Commentary was that it is a mistake–and an impoverishment of human science–to regard these emphases as contradictory; and that no known facts require either interactionist or materialist postulates to do them justice. (p. 454)
 It is important to note that Popper and Eccles argued that the interaction between mind and brain is only necessary for events of which the person is consciously aware. For subconscious tasks, such as controlling digestion or maintaining heart rate, they were willing to admit that the brain may function mechanically.
 There are some striking similarities between MacKay’s two columns and David Chalmer’s double-aspect theory of information (Chalmers, 1995).
TABLE I. MacKay’s two types of data
Legend for chart:
A - Data from experience (I-story)
B - Data from brain activity (brain-story)
I feel my mouth moving Neural activity A
I hear my own voice Neural activity B
I see a room full of people Neural activity C
I think that interactionism is silly Neural activity D
I believe that some people are following
my argument Neural activity E
I know that I have about ten minutes left Neural activity F
I remember the first time I saw Donald
MacKay use these columns Neural activity G
ANDREASEN, N.C. (1997). Linking mind and brain in the study of mental illnesses: a project for a scientific psychopathology. Science, 275, 1586-1593.
BUNGE, M. (1977). Emergence and the mind. Neuroscience, 2, 501-510.
BUNGE, M. (1979). The mind-body problem, information theory, and Christian dogma. Neuroscience, 4, 453.
BUNGE, M. (1980). The mind-body problem: A psychobiological approach. Oxford: Pergamon.
CHALMERS, D. (1995). Facing up to the problem of consciousness. Journal of Consciousness Studies, 2, 200-219.
MACKAY, D.M. (1978). Selves and brains. Neuroscience, 3, 599-606.
MACKAY, D.M. (1979). Reply to Bunge. Neuroscience, 4, 454.
POPPER, K.R. & ECCLES, J.C. (1977). The self and its brain: An argument for interactionism. Berlin: Springer.
By THOMAS E. LUDWIG