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24. A Critical Note on Parallelism. The Identity Theory as a Form of Parallelism.

In this section I am going to discuss what one may describe as the empirical background of psycho-physical parallelism. By way of an afterthought, I shall suggest that whatever may appear as a piece of supporting evidence in favour of the identity theory is also one of the cases which seem to support parallelism; an additional reason for interpreting the identity theory as a special case (a "degenerate case") of parallelism.

I shall start from the relation of perception to the other contents of our consciousness, and I shall try to throw some light on certain characteristics of perceptions by discussing the biological function of perception.

Under the influence of Descartes and also of British empiricism, a kind of atomistic theory of mental events or processes became widely established. In its simplest form, this theory interpreted consciousness as a sequence of elementary ideas. It does not matter for our purposes whether the ideas were regarded as unanalysable atoms, or as molecular (and consisting, say, of atomic sensations or of sense data or what not). What is important is the doctrine that there are elementary mental events ("ideas") and that the stream of consciousness consists of an ordered sequence of such events.

Some of the Cartesians then assumed that to each elementary mental event there corresponds a definite brain event. This correspondence was assumed to be of the one-to-one kind. The result is mind-body parallelism, or psycho-physical parallelism.

Now it is to be admitted that there is a kernel of truth in this theory. When I look at a red flower, then (keeping still) close my eyes for a second, and then open them and look again, the two perceptions will be so similar that I recognize the second perception as a repetition of the first. We all assume that this repetition is to be explained by the similarity of the two temporally distinct irritations of my retina, and of the two corresponding brain processes. If we generalize from such considerations (a generalization which to a Humean, particularly, may appear valid, since for Hume all consciousness consists only of such experiences) we arrive at psycho-physical parallelism. (The Gestalt switch of a Necker cube1 which, no doubt, is due to changing functioning of the brain would seem to add further confirmation.)

It is therefore understandable why psycho-physical parallelism appears so convincing, indeed obvious, to many. Nevertheless I shall try to combat it here. My fundamental objection will be that the examples of repeated perceptions have been misinterpreted, and that our states of consciousness are not to be thought of as sequences of elements — neither of atoms nor of molecules.

True: I did look twice, with attention, at the same object; and since my mind has learned how to inform me about my environment, it informed me of this fact. It did so by producing the hypothesis, or the conjecture: "This is the same flower as before (and the same aspect of it, since neither the flower nor I have moved)."

But it is precisely because I was thus informed when I allegedly "identified the two experiences" that the second experience or state of consciousness was different from the first. The identification was one of objects, and of their aspects. The subjective experience (the "judgement" formed, the conjecture formed) was different: I experienced a repetition, which with the first I did not. If this is so, then the theory of consciousness as a sequence of (often repetitive) elementary or atomic perceptions is mistaken. And in consequence, the theory of a one-to-one correspondence between elementary conscious events and brain events will have to be given up as baseless (though certainly not as empirically refuted). For if our states of consciousness are not sequences of elements, then it is no longer clear what is supposed to correspond to what, in a one-to-one manner.

A parallelist might try to avoid this conclusion, insisting that our perceptions (and the corresponding brain events) are not atomic but molecular: in this case, the (postulated) experiential atoms and elements of the objective brain events may still be in one-to-one correspondence, although there may perhaps in fact never be two molecular experiences (and their corresponding brain events) which are identical.

It seems to me that two points may be made against such a view.

First, while the original theory which we were discussing was straightforward and informative, describing, as it did, actual experiences as elementary or atomic perceptions, and suggesting that there was some elementary brain event in one-to-one correspondence with each of these, we are now offered an atomistic ghost as a replacement. For the replacement theory is completely speculative, merely alleging that all actual experiences are composed in some unspecified way of atomic components, to which there are supposed to be brain correlates: it transfers atomism dogmatically from physics to psychology. Such things may exist — we cannot rule them out — but such a theory cannot claim any empirical support.

Second, considered as a theory of perception, I think that it is on the wrong track. I shall suggest below that we should take a biological approach to consciousness, and that one of the functions of consciousness is to allow us to recognize physical objects when we meet them again. This is arbitrarily interpreted by the theory we have been discussing as the recurrence of a psychological event and a corresponding brain event.

(The theory of perception which I am criticizing is, incidentally, a part of the very popular but nevertheless mistaken theory of a one-to-one correspondence between stimulus and response, or between input and output; and this theory, in its turn, is part of the theory, apparently upheld by Sherrington in [1906], but rejected by him in [1947], that there is one elementary kind of atomic or molecular brain function — the "reflexes" and the so-called "conditioned reflexes" — of which all the others are complexes or integrations. See Roger James [1977].25)

What, then, of the status of perception? I suggest that we proceed in a different way. Instead of starting from the assumption of a one-to-one stimulus response mechanism (though such mechanisms may perhaps exist and may perhaps even play an important role), I suggest that we start from the fact that consciousness or awareness has a number of biologically useful functions.

If we regain consciousness after a spell of unconsciousness, a typical problem arises: "Where am I?". I take this as an indication that it is an important function of consciousness to keep track of our whereabouts in the world by constructing a kind of schematic model (as Kenneth J.W. Craik [1943] suggested) or a schematic map; detailed as far as our momentary immediate environment is concerned, but very sketchy as far as more distant regions are concerned. This model or map, I suggest, with our own position marked on it, is part of our ordinary consciousness of self. It normally exists in the form of vague dispositions or programmes; but we can focus our attention upon it whenever we wish, whereupon it may become more elaborate and precise. This map or model is one of a great number of conjectural theories about the world which we hold and which we almost constantly call to our aid, as we go along and as we develop, specify, and realize, the programme and the timetable of the actions in which we are engaged.

If we now look at the function of perception with this in mind then, I suggest, our sense organs should be regarded as auxiliaries to our brain. The brain in turn is programmed to select a fitting and relevant model (or theory or hypothesis) of our environment, as we move along, to be interpreted by the mind. This I should call the original or primary function of our brain and of our sense organs — in fact, of the central nervous system: in its most primitive form it developed as a steering system; as an aid to movement. (The primitive central nervous system, in worms, is an aid to movement; and so are the far more primitive senses of fungi. See Max Delbrueck [1974] for a report of his fascinating investigations into the beginning of sense organs in phycomycetes.)

The frog is programmed for the highly specialized task of catching moving flies. The frog's eye does not even signal to its brain a fly within reach if it does not move.3

Many years ago I quoted David Katz (Animals and Men, chapter VI; see my [1963 (a)], pp. 46f.) in a similar context: "A hungry animal divides the environment into edible and inedible things. An animal in flight sees roads to escape and hiding places." In general, an animal will perceive what is relevant according to its problem situation; and its problem situation, in turn, will depend not only on its external situation, but upon its inner state: its programme, as given by its genetic constitution, and its many sub-programmes — its preferences and choices. In the case of man, this involves personal aims and personal, conscious decisions.

Looking back from here to our experiment which led to a sequence of two practically identical perceptions, I do not deny that the two perceptions were extremely similar qua perceptions: our brain, supported by our eyes, would not have done its biological duty had it not informed us that our environment did not change from the first instant of time to the second. This explains why in the field of perception there will be a consciousness of repetition if the objects perceived do not change, and if our programme does not change. But this does not mean that the content of our consciousness was repeated, as I have already hinted. Nor does it mean that the two brain states were very similar. In fact, our programme (which was, in this special case, "compare your response to a stimulus repeated in two consecutive instants of time") did not change between the first instant and the second. But the two instants of time played decidedly different roles in that programme, just because of the repetition; and this alone ensured that they were experienced in different ways.

We now see that, even as far as the consciousness of perceptions is concerned (which represents only a part of our subjective experiences) there is no one-to-one correspondence of stimulus and response, as indicated by David Katz's remark about possible changes in our interest and in our attention. Nevertheless, perceptions would not fulfil their task unless, in cases when interest and attention did not change, there was there something approaching to a one-to-one correspondence. But this is a very special case. And the usual procedure of generalizing from this special case, and of looking at stimulus and response as a simple one-to-one mechanism, and of confining the contents of our conscious experiences to this, is grossly mistaken.

But if we discard the idea of two one-to-one correlated sequences of events, the idea of psycho-physical parallelism loses its main prop. This does not refute the idea of parallelism, but it dissolves, I think, its apparently empirical basis.

Incidentally, the theory of brain-mind identity turns out, in the light of the present considerations, to be a special case of the idea of parallelism; for it too is based on the idea of a one-to-one correlation: it is an attempt rationally to explain this one-to-one correlation which it takes, uncritically, for granted.

1 The following seems to work with most people: if we stare for long enough at a diagram of a Necker cube, then it switches on its own into the opposite interpretation (that is, with that side which previously looked at the front now appearing to be at the back). The effect may be related to the tendency for anything to disappear if we have stared at it for long enough. This tendency, and perhaps with it the former effect, can be explained biologically. It is well known that a not too loud noise disappears subjectively after a time, unless we draw our attention to it consciously See also note 2, below.

25  See also section 40. In this context, reference should be made to the experiments which show that stabilized images, stabilized noises, and stabilized touches (for example from our clothes) show a tendency to fade. For clearly the fading effect depends upon something like physical or stimulational similarity. But as this leads to fading, there is a dissimilarity of response.

3 See Lettvin & others [1959].

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