Top-Down Causality

Those who hold views of the soul that originate in the Semitic traditions would not generally want to hold that the world of inner experience could exist entirely on its own, without any identifiable form of physical embodiment or context. But they would want to assert the possibility of different forms of embodiment and of a transfer of the inner experiences of a conscious being into differing environments (the "resurrection world").

So, it is important for them to believe that there really is an inner world of experience and that, in it, there originate morally significant causal intentions and acts that are not determined by physical states alone. The views of the neuropsychologists just outlined seem to support such a possibility. Such views, therefore, seem to rebut reductive physicalism—a physicalism that asserts that humans are "nothing but" physical organisms. There is a more subtle view, however, well propounded by Warren Brown (Brown, Murphy, and Malony 1998), what he calls "nonreductive physicalism." This, at first sight, seems to fit well with some Semitic beliefs about resurrection, but I doubt whether it is, in the end, helpful to call it a form of physicalism at all. According to this view, humans are purely physical beings, but thoughts, feelings, and perceptions are higher-level emergent properties of brains that have causal effects on the complex physical systems that are human beings. They are examples of what Warren Brown and Nancey Murphy, his coauthor, call "top-down causation."

Examples of top-down causation are extensive in biomedical and psychological literature. They include energy metabolism in mitochondria, by which a wider physical system governs or influences the processes that take place in intact cells; the production of three-dimensional information from two-dimensional images in visual perception; and the influence of working memory on the activity of neurons of the temporal lobe.

Warren Brown argues that there is no need to introduce any such entity as the soul, which he sees as an immaterial agent. Mental acts are causally influenced by neural systems to a very great extent. There is very little left, he says, for an allegedly immaterial "soul" to do. "The concept of a nonmaterial human 'soul' or 'spirit' as a causal force within the mental and behavioral life of a person is difficult to reconcile with what can be demonstrated scientifically about the impact of changes in brain systems on thought and behavior" (2004, 76). Nevertheless, he says, "conscious decisions and will are real phenomena that are effective in exerting a top-down (or whole—part) causal influence on the neurophysiological processes of the brain" (63). The patterns that emerge from complex physical systems have genuine causal powers. There are no new "entities" or physical forces involved, but there are new "levels of causal efficacy" (65).

The two beliefs—that there is not much causal work for a soul to do and that there are new causal powers in complex systems—are in some conflict with each other. It is incontestable that neural function is a necessary condition of mental activity in humans and that impairment of neural function leads to impairment of mental activity. But if there is any new causal efficacy in the brain, that is just what the soul is supposed to do. As long as there are consciously directed thoughts, deeply appreciated feelings, and attentive perceptions, there will be top-down causal activity. So, the objection that there is little for a soul to do seems very weak. The soul does precisely whatever higher mental functions do.

Still, it might be said, such functions make a soul superfluous. Why not just stick to top-down causality, and drop any talk of mental entities? But if you do that, what happens to "the colorful and value rich world of inner experience" of which Roger Sperry spoke? If it is not to disappear, and leave us with reductive materialism, we will have to say that there is more to physical entities than the publicly observable, colorless, value-free world of flickering subatomic particles of which physics speaks.

We might not want to call the colors, sounds, and smells we all subjectively experience "entities," as though they were objects in a shadow universe paralleling the physical universe. But they are appearances that are different from the world that is the causal object of their appearing. They are appearances of the world to consciousness, and consciousness itself is the way the world appears in immediate experience.

The problem with the whole—part model is that the whole must be composed of the same sort of stuff as the parts, however complex it gets. Sixty-five million colorless elementary particles, put together in a complex way, do not make up a single spot of color. They may, however, in a neocortex, cause the appearance of color and cause us to say that sixty-five million other particles that we are observing are colored in a certain way. The appearance of color is caused by complex causal processes, and it is the appearance of a complex causal process.

A tree looks green when observed by a human brain with functioning visual perceptual equipment. The green is not itself a complex brain system, which includes neurons as its smaller parts. So the whole—part model does not quite seem to fit. Rather, when one physical system causally interacts with another complex physical system, a green appearance of a tree comes into existence. The tree looks green; it is green when it interacts with a human brain and visual system.

We can identify the green with the physical tree, but only as seen by a human observer. In the same way, the brain looks gray, as seen by a human observer. When the brain undergoes neural activity, can we say that it thinks? Perhaps that is how its activity appears to the owner of the brain. But, again, this does not seem to be a case of a wider system influencing its smaller parts. If thoughts are appearances of neural events, it is rather that the thoughts are produced by neural events, and those thoughts sometimes cause the brain to be in some neural states rather than others.

The philosopher Jaegwon Kim (1994) has argued that once mental causality is admitted, physicalism has, in effect, been given up, and we have a dualist view of spirit and matter, no matter how much scientists dislike the thought. The question of causal efficacy is crucial. Are the only efficacious causal events physical, publicly observable, and measurable? If so, mental events are epiphenomena, with no real causal role. But if thinking can causally influence brain states, this is not a case of wider physical systems influencing smaller parts of themselves. It is a case of neural processes being influenced by states of consciousness. In other words, some sort of dualism seems inescapable. This is not really physicalism—the theory that nothing but physical entities exist—at all, even if it is called "nonreductive."

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