Competing for Consciousness:A Darwinian Mechanism--论文代写范文精选

弗朗西斯·克里克提出,人们曾担心生命和非生命物质之间的边界。今天,边界似乎没有意义;我们不是谈论所有的分子生物学。今天的大脑研究人员认为它可能提供科学和哲学的关注。下面的essay代写范文进行详述。

Abstract
Treating consciousness as awareness or attention greatly underestimates it, ignoring the temporary levels of organization associated with higher intellectual function (syntax, planning, logic, music). The tasks that require consciousness tend to be the ones that demand a lot of resources. Routine tasks can be handled on the back burner but dealing with ambiguity, groping around offline, generating creative choices, and performing precision movements may temporarily require substantial allocations of neocortex. Here I will attempt to clarify the appropriate levels of explanation (ranging from quantum aspects to association cortex dynamics) and then propose a specific mechanism (consciousness as the current winner of Darwinian copying competitions in cerebral cortex) that seems capable of encompassing the higher intellectual function aspects of consciousness as well as some of the attentional aspects. It includes features such as a coding space appropriate for analogies and a supervisory Darwinian process that can bias the operation of other Darwinian processes.

Francis Crick likes to observe that people once worried about the boundary between the living and the nonliving. Today, the boundary seems meaningless; we instead talk about all the varied aspects of molecular biology. Today's brain researchers think it likely that much of the present scientific and philosophical concern about consciousness will soon become equally obsolete, that we will simply come to talk of the various physiological processes involved with attention and creative problem-solving. 

This is not to say that consciousness will disappear as a useful word in our vocabularies. Nor will the philosophers' cautions about classical mistakes cease to be relevant. Just as "living" has continued to be a useful shortcut, so will "conscious" and "mind." Even those of us who come to understand all the contributing physiological processes will still need the C word, not only for communicating with those outside the field but even for thinking about the subject.

So let me attempt a neurophysiologist's introduction to the subject, one that I hope will remain useful as we build our knowledge about what Dan Dennett called "the last surviving mystery." A mystery, Dennett said, "is a phenomenon that people don't know how to think about -- yet." Here I will attempt to clarify the appropriate levels of explanation and then propose a candidate mechanism, a Darwin Machine (Calvin 1987, 1996) that seems capable of encompassing the higher intellectual function aspects of consciousness as well as some of the attentional aspects. [Portions of this article are adapted from my two 1996 books, How Brains Think (Basic Books, New York) and The Cerebral Code (MIT Press, Cambridge MA).].

Consciousness is the tip of the iceberg, in the sense that many other things are going on in the brain at the same time, hidden from view. Indeed, we are incapable of reporting on most of what our brain does for us. I cannot report on my blood pressure without a lot of external instrumentation, even though my brain measures and regulates my systolic and diastolic pressures. It is simply not accessible for verbal reporting.

For the brain, we need to span multiple levels of mechanism -- from synapses to cells to circuits to modules, and more. And also span multiple levels of phenomenological explanation -- such as attributes, objects, categories, analogies, and metaphors. Layers of middlemen are familiar from everyday economics, and we expect to see many layers of representation standing between our consciousness and the real world. As Derek Bickerton noted:

[T]he more consciousness one has, the more layers of processing divide one from the world. . . . 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.There are subconscious trains of thought, however, and they vie for "attention." The layer immediately underlying consciousness might well involve a mechanism for competition.

Though the obvious analogy is to the television viewer who surfs the channels (and our nighttime dreams often seem like switching between soap operas in progress), there need not be a central place where choices are viewed. The "best" channel need only temporarily win out over the others in the battle for access to output pathways such as speech and other body movements. Soon, another channel comes to dominate and we speak of "our attention shifting" -- but there need not be an agent which makes the decision or performs the action, not any more than ice needs an agent to help it melt.

Output need not involve overt movements: silent speech is an important way in which we reason, generate alternatives, and choose amongst them. The mental rotation of complex objects illustrates a nonlanguage mode of conscious thought. But, to a neurophysiologist, there is nothing in this overview that demands a central place. The "center of consciousness" could, instead, shift from moment to moment: from language to nonlanguage areas, from frontal to parietal lobe, from left to right hemisphere, and maybe even from cortical to subcortical structures -- anywhere, I suspect, with the potential for generating novel patterns of movement. And, of course, it seems possible to do several things at once, just as one can sew, or listen to the radio, while watching television. Not everything we do has to pass through the current center of consciousness.

Karl Popper noted that posing alternatives seemed especially “conscious”:
Much of our purposeful behaviour (and presumably of the purposeful behaviour of animals) happens without the intervention of consciousness.... Problems that can be solved by routine do not need consciousness. [The biological achievements that are helped by consciousness are the solution of problems of a non-routine kind.] But the role of consciousness is perhaps clearest where an aim or purpose... can be achieved by alternate means, and when two or more means are tried out, after deliberation.

While I think that Popper is on to something here, I'd state it more generally: the tasks that require consciousness tend to be the ones that demand a lot of resources. Routine tasks can be handled on the back burner but dealing with ambiguity, groping around, generating creative choices, and performing precision movements may temporarily require substantial allocations of neocortex.

Consciousness and Levels of Explanation
What constitutes an explanation? To explain consciousness in any serious way, we must avoid using mathematical concepts to dazzle rather than enlighten. And we must watch out for "proofs by want of imagination," as when we conclude, out of arrogance or impatience, that there are no other alternatives to the answers we have found. When it comes to the brain, in particular, we must be careful to pitch our theories at the right level of mechanistic explanation.

Brain function involves at least a dozen levels, and finding appropriate levels for aspects of consciousness has not been easy. Everyone tends to extrapolate their favorite subject of study and proclaim its relevance to consciousness. Since I'm about to do the same thing myself, indulge me in a few words about levels, particularly as they relate to emergent properties and those "changes of state," for I have two major points to make in this short summary of (and borrowing from) my longer works, How Brains Think and The Cerebral Code. One is a proposal for a specific consciousness mechanism (as the current winner of Darwinian copying competitions in association cortex) and the other is an argument about what's a correct level at which to seek a consciousness mechanism. I hope both are correct, but the level analysis ought to be more generally useful; it's certainly intended as a critique of much that has been written on the subject.

What's missing from most discussions of consciousness is, surprisingly, the whole concept that there are levels of explanation. Douglas Hofstadter (1985) gives a nice example of levels when he points out that the cause of a traffic jam is not to be found within a single car or its elements. Traffic jams are an example of self-organization, more easily recognized when stop-and-go achieves an extreme form of quasi-stability -- the crystallization known as gridlock. An occasional traffic jam may be due to component failure, but faulty spark plugs aren't a very illuminating level of analysis-- not when compared to merging traffic, comfortable car spacing, driver reaction times, traffic signal settings, and the failure of drivers to accelerate for a hill or high-rise bridge.

The more elementary levels of explanation are largely irrelevant to traffic jams. Such decoupling was emphasized by the physicist Heinz Pagels (1988), who noted:
“Causal decoupling” between the levels of the world implies that to understand the material basis of certain rules I must go to the next level down; but the rules can be applied with confidence without any reference to the more basic level. Interestingly, the division of natural sciences reflects this causal decoupling. Nuclear physics, atomic physics, chemistry, molecular biology, biochemistry, and genetics are each independent disciplines valid in their own right, a consequence of the causal decoupling between them.... Such a series of “causal decouplings” may be extraordinarily complex, intricate beyond our current imaginings. Yet finally what we may arrive at is a theory of the mind and consciousness — a mind so decoupled from its material support systems that it seems to be independent of them — and “forgot” how we got to it.... The biological phenomenon of a self-reflexive consciousness is simply the last of a long and complex series of “causal decouplings” from the world of matter.

Stratified Stability and Emergents
Closely related is the notion of emergent properties: traffic jams and crystals emerge from combinations, and we expect emergence to play a large role in the transient levels of organization involved with higher intellectual function (language, planning, games, etc.). In our search for a level corresponding to consciousness, it is well to recall that levels arise from what Jacob Bronowski (1973) called stratified stability:
Nature works by steps. The atoms form molecules, the molecules form bases, the bases direct the formation of amino acids, the amino acids form proteins, and proteins work in cells. The cells make up first of all the simple animals, and then the sophisticated ones, climbing step by step. The stable units that compose one level or stratum are the raw material for random encounters which produce higher configurations, some of which will chance to be stable.... Evolution is the climbing of a ladder from simple to complex by steps, each of which is stable in itself.

The tumult of random combinations occasionally produces a new form of organization. Some forms, such as the hexagonal cells that appear in the cooking porridge if you forget to stir it, are ephemeral (as, indeed, are the contents of our consciousness). Other forms may have a "ratchet" that prevents backsliding once some new order is achieved.

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