A book by William H. Calvin UNIVERSITY OF WASHINGTON SEATTLE, WASHINGTON 98195-1800 USA |
HOW BRAINS THINK
A Science Masters book, to be available in 12 translations (BasicBooks in the US) copyright ©1996 by William H. Calvin |
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How should we approach explaining the unknown? It is well to keep overall strategy in mind,
especially whenever attractive shortcuts are offered as explanations by those whom the
philosopher Owen Flanagan terms ``the new mysterians.'' Using Dennett's epigrammatic
definition of a mystery, consider for a moment those physicists who are speculating about how
quantum mechanics might have a role in consciousness, might provide ``free will'' an escape
route from ``determinism'' via quantum mechanical processes down at the subcellular level, in
the thin microtubules that often cluster near synapses. I'm not going to take the space needed to do justice to their best-selling arguments (or rather the arguments of their best-selling books), but when you consider how little they actually encompass (let alone explain) of the wide range of themes involved in consciousness and intelligence (those previous two chapters), you might feel, as I do, that they're just another case of ``much ado about very little.'' Moreover, as chaos and complexity have been teaching us, determinism is really a nonissue, suitable only for cocktail party conversational gambits and hardly in need of a quantum mechanical escape clause. With some notable exceptions (I'll them ecclesiastic neuroscientists after the great Australian neurophysiologist John C. Eccles), neuroscientists seldom say similar things; indeed, we rarely engage in such word games about consciousness. It's not for lack of interest; how the brain works is, after all, our primary preoccupation. Over our beers after a hard day at the neuroscience meetings, we tell each other that while we may not have wide-ranging explanations of consciousness yet, we do know what kinds of explanations don't work. Word games produce more heat than light, and the same is true of explanations that simply replace one mystery with another. Neuroscientists know that a useful scientific explanation for our inner life has to explain more than just a catalog of mental capabilities. It also has to explain the characteristic errors that the consciousness physicists ignore -- the distortions of illusions, the inventiveness of hallucinations, the snares of delusions, the unreliability of memory, and our propensities to mental illnesses and seizures rarely seen in other animals. An explanation has to be consistent with many facts from the last century of brain research-- with what we know about consciousness from studies of sleep, strokes, and mental illness. We have numerous ways of ruling out otherwise attractive ideas; I've heard a lot of them in thirty years of doing brain research. |
There are various angles along which to cut the cake of our mental lives. I tried focussing on
consciousness in The Cerebral Symphony. One reason that I'm going to hereafter avoid a
discussion of consciousness in favor of intelligence underpinnings is that considerations of
consciousness quickly lead to a passive observer as the end point, rather than someone who
explores, who adventures within the world. You can see that in the many ``consciousness''
connotations you'll find in a dictionary:
Among scientists, there is a tendency to use consciousness to mean awareness and recognition; for example, Francis Crick and Christof Koch use consciousness when addressing the ``binding problem'' in object recognition and recall. But just because one word (in English) is used to denote these widely different mental facilities doesn't mean that they share the same neural mechanism. Other languages, after all, may assign one of the aforementioned ``consciousness'' connotations its own word. Crick's thalamocortical theory is most useful for thinking about object recognition but it doesn't say anything about anticipation or decisionmaking -- yet those are often among the connotations of consciousness, the word he uses. It's easy to overgeneralize, just by the words you choose. This isn't a criticism: there aren't any good choices until we understand mechanisms better. By now, the reader might reasonably conclude that consciousness connotations are some sort of intelligence test that examines one's ability to float in ambiguity. Debates about consciousness regularly confuse these connotations with one another, the debaters acting as if they believed in the existence of a common underlying entity -- ``a little person inside the head''-- that sees all. To avoid this presumption of a common mechanism for all connotations, we can use different English words for different connotations, such as when we use ``aware'' and avoid ``conscious.'' I usually try to do this, but there are also pitfalls when you use alternative words. That's because of what might be termed back-translation. Physicians, for example, try to avoid the C word by talking instead about the level of arousal that can be achieved with some shouting and prodding (coma, stupor, alert, or fully oriented to time and place) of the patient. That's fine, until someone tries to translate back into C-word terminology; yes, someone in a coma is unconscious, but to say that consciousness is at the opposite end of the arousability scale may be seriously misleading. Worse, equating ``conscious'' with ``arousable'' tends to be interpreted as ascribing consciousness to any organism that can experience irritation. Since irritability is a basic property of all living tissue, plant as well as animal, this extends consciousness to almost everything except rocks; some nonscientists are already talking about plant consciousness. While this is appealing to some people and appalling to others, scientifically it is simply bad strategy (even if true). If you throw everything into the consciousness pot and mix them up, it reduces your chances of understanding consciousness. With so many major synonyms (aware, sensitive, awake, arousable, deliberate, and more), you can see why everyone gets a little confused talking about consciousness. One often hears the word's connotation shift in the course of a single discussion; were this to happen to the word ``lift,'' with one speaker meaning what hitchhikers get and the other meaning an elevator, we'd burst out laughing. But when we talk about consciousness, we often fail to notice the shift (and debaters even exploit the ambiguity to score points or sidetrack the argument). And there's more: at least within the cognitive neuroscience community, consciousness connotations include such aspects of mental life as the focusing of attention, vigilance, mental rehearsal, voluntary actions, subliminal priming, things you didn't know you knew, imagery, understanding, thinking, decision making, altered states of consciousness, and the development of the concept of self in children -- all of which grade over into the subconscious as well, all of which have automatic aspects that our ``narrator of consciousness'' may fail to notice. Many people think that the narratives we tell ourselves when awake or dreaming tend to structure our consciousness. Narratives are an important part of our sense of self, and not merely in an autobiographical sense. When we play a role-- as when the four-year-old engages in make-believe, playing ``doctor'' or ``tea party''-- we must temporarily step outside of ourselves, imagine ourselves in someone else's place, and act accordingly. (The ability to do this is one of the more useful definitions of a sense of self.) But narratives are an automatic part of everyday life in our own skins. Starting around the age of three or four, we make stories out of most things. Syntax is often a junior version of narrative: just the word ``lunch'' in a sentence sends us looking for variants of the verb ``eat,'' for the food, the place, and persons present. A verb such as ``give'' sends us searching for the three required nouns we need to fit into roles: an actor, an object given, and a recipient. There are lots of standard relationships, with familiar roles for the players, and we guess from the context what goes into any unfilled gaps. Often we guess well, but dreams illustrate the same kinds of confabulation seen in people with memory disorders, in which bad guesses are unknowingly tolerated.
``Perception,'' it has been recently said, ``may be regarded as primarily the modification of an anticipation.'' It is always an active process, conditioned by our expectations and adapted to situations. Instead of talking of seeing and knowing, we might do a little better to talk of seeing and noticing. We notice only when we look for something, and we look when our attention is aroused by some disequilibrium, a difference between our expectation and the incoming message. We cannot take in all we see in a room, but we notice if something has changed. |
A sense of self is thought to go along with a fancy mental life, so let me briefly address
the common notion that self-awareness (often called self-consciousness) involves
sophisticated, ``intelligent'' mental structures. How do you know which muscles to move in order to mimic the action of someone else -- say, in order to stick out your tongue in response to seeing such an action? Do you have to see yourself in a mirror first, to make the association between that sight and the muscle commands that will mimic it? No. Newborn humans can imitate the facial expressions they see, without any such experience. This suggests that innate wiring connects at least some sensory templates with their corresponding movement commands, that we're ``wired to imitate'' to some extent. Such wiring might explain why some animals can recognize themselves in a mirror, while others treat their mirror image as another animal, to be coaxed or threatened. Chimps, bonobos, and orangs can recognize themselves either immediately or within a few days' experience; gorillas, baboons, and most other primates cannot. A capuchin monkey (Cebus are the most intelligent of the New World monkeys and the best tool users) with a full-length mirror in its cage may spend weeks threatening the ``other animal.'' Ordinarily, one animal would back down after a brief period, acknowledging the other as dominant. But in the case of the mirror monkey, nothing is ever resolved; even if the capuchin tries acting submissive, so does the other animal. Eventually the monkey begins acting so depressed at the unresolved social conflict that the experimenters must remove the mirror. What might self-recognition involve? Actions produce expectations about what sensory inflow will result from them (so-called efference copy) and so the perfect fit of these sensory predictions during small movements with the inputs from your skin and muscles would provide a way of recognizing yourself in an image. The perfect fit of the mirror image's movements with internal predictions would certainly be unusual for facial movements in most wild animals, since they rarely see their own face. The issue of self-consciousness in the animal literature could revolve about something as simple as the attention paid to predictions about facial sensations. That's part of consciousness considerations, surely, but hardly the pivot that some would make it. Self-recognition surely involves both Horace Barlow's guessing right and Jean Piaget's sophisticated groping, but I'd put it on the list of things that intelligence isn't. Self-recognition is surely more to the point than quantum fields, however. |
There's a second neuroscience ghost story: the philosopher Gilbert Ryle's lovely
phrase ``the Ghost in the Machine'' refers to the little-person-inside manner in which
we commonly refer to the ``us'' inside our brains. It has led some researchers to talk
about the ``interface'' between ``mind'' and brain, between the unknowable and the
knowable. Is this just Descartes's pineal gland proposal dressed up in modern clothes
by the new mysterians? We're now making good progress in replacing such pseudospirits with better physiological analogies -- and, in some cases, with actual brain mechanisms. Just as an earlier generation of scientists usefully eliminated the external ghosts, I like to think that our currently evolving knowledge about the spirit substitutes will help people think more clearly about themselves and interpret their experiences more reliably, and will help psychiatrists to interpret the symptoms of mental illness. The consciousness physicists, with their solution in search of a problem, surely aren't intending to tell yet another ghost story. They're just having a good time speculating, in the manner of science-fiction writers. (Still, consider how odd it would be for neuroscientists to speculate about the enigmas of physics, even those neurophysiologists -- and there are many -- who once took several courses in quantum mechanics). But why do these physicists take themselves so seriously, when a dozen levels of organization outside their own specialties? Specialization itself is perhaps part of the answer, and it demonstrates one of the hazards of intelligence. |
Describing our mental lives has a well-known hang-up, the old subjectivity snare
associated with point of view, but there are two other whirlpools we will also need to
navigate around. The passive observer, poised in the middle between sensation and action, is a point of view that leads to all sorts of needless philosophical trouble. Partly, that's because sensation is only half of the loop, and we thereby ignore sensation's role in preparing for action. Some of the more elaborate couplings of sensation to action are called ``cortical reflexes'' but we also need to understand how thought is coupled to action in an intelligent manner, when we grope for a novel course of action. Ignoring the mental middle, as the behavioral psychologists did a half century ago, is not a long-term solution. What neuroscientists often do is to investigate the preparation for movement; that gets us somewhat closer to the thought process. We often talk of our mental activities as being subdivided between sensing, thinking, and acting phases. But trouble arises because few things happen at one point in time and space. All of the interesting actions in the brain involve spatiotemporal patterns of cellular activity-- not unlike what constitutes a musical melody, where the space is the keyboard or musical scale. All our sensations are patterns spread out in time and space, such as the sensation from your fingers as you get ready to turn to the next page. So too, all our movements are spatiotemporal patterns involving the different muscles and the times at which they are activated. When you turn the page, you are activating about as many muscles as you use in playing the piano (and unless you get the timing just right, you won't be able to separate the next page from the rest). Still, we often try to understand mental events by treating them as if they actually occurred at one place and happened at one instant. But what's in the mental middle is also a spatiotemporal pattern-- the electrical discharges of various neurons-- and we shouldn't count on it being funneled through one point in space (such as a particular neuron) and a decision made at one point in time (such as the moment when that particular neuron discharges an impulse), as if a perception or thought consisted of playing a single note, once. I know of only one such case in vertebrates (occasionally nature makes things convenient for neurophysiologists): it's an escape reflex in fish, conveniently channeled through a single large brain-stem neuron, whose discharge initiates a massive tail flip. But higher functions inevitably involve large overlapping committees of cells, whose actions are spread out in time, and that's a more difficult concept. Understanding higher intellectual function requires us to look at the brain's spatiotemporal patterns, those melodies of the cerebral cortex. |
In addition to the navigational hazards, we will need to select our building blocks
with care so that we don't simply replace one mystery with another. Premature closure
is the most obvious hazard to selecting building blocks, where we stop surveying
candidate mechanisms too early, as when explaining via spirits or quantum fields. We must also beware of several other hazards having to do with end points of an ``explanation'': the new age everything-is-related-to-everything and the reductionistic explanations at an inappropriate level of organization (what the consciousness physicists and ecclesiastic neuroscientists do, in my not-so-humble opinion). Explaining mental life is a big task, and you may have noticed that this is a reasonably thin book. As noted, instead of further exploring consciousness connotations, I'm going to cut the cake differently, focusing on the structures of our mental lives that are associated with intelligence. Intelligence is all about improvising, creating a wide repertoire of behaviors, ``good moves'' for various situations. A focus on intelligence covers a lot of the same ground as does a focus on consciousness -- but it avoids many of the navigational hazards. Most important, the good-moves repertoire is an end point very different from the snapshots of passive contemplation. Certainly it's easier to find a continuity between ourselves and the rest of the animal kingdom by addressing the subject of intelligence, compared to the muddle we generate when we try to talk about animal ``consciousness.'' And so the next task is to take a brief look at where good guessing might have come from, in evolutionary terms.
The paradox of consciousness -- that the more consciousness one has, the more layers of processing divide one from the world -- is, like so much else in nature, a trade-off. Progressive distancing from the external world is simply the price that is paid for knowing anything about the world at all. The deeper and broader [our] consciousness of the world becomes, the more complex the layers of processing necessary to obtain that consciousness.
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