shadows on that wall, the B-brain mistakes A’s descriptions for real things, not knowing what they might actually mean. What the B-Brain sees as its ‘outer world’ are only events in the A-brain itself.
Neurologist: And that also applies to you and me. For, whatever you think you touch or see, the higher levels of your brain never can actually contact these—but can only interpret the representations of them that your other resources construct for you.
When the fingertips of two ardent lovers come into intimate physical contact, no one would claim that this, by itself, has any special significance. For there is no sense in those signals themselves: their meanings to each lover lies in each one’s representations of the other one’s mind.[75] Nevertheless, although the B-Brain cannot directly perform a physical act, it still could affect the external world, albeit indirectly—by sending signals that change how A will react. For example, if A gets stuck at repeating itself, it might suffice for B just to interrupt.
Student: Like when I’ve misplaced my spectacles, I tend to keep seeking it on the same shelf. Then a silent voice reproaches me, suggesting that I look somewhere else.
In the ideal case, B could tell (or teach) A exactly what it ought to do. But even if B does not have such specific advice, it might not need to tell A what to do; it may suffice only to criticize the strategy A is using now.
Student: But what if I were walking across a road, when suddenly my B-brain said “Sir, you’ve repeated the same actions with your leg for more than a dozen consecutive times. You should stop right now and do something else.”
Indeed, that could cause a serious accident. To prevent such mistakes a B-Brain must have appropriate ways to represent things. This accident would not occur if B represent ‘walking to a certain place’ as a single extended act—as in “Keep moving your legs till you’ve crossed that street”—or in terms of progress toward some goal—as in, ‘keep reducing the remaining distance.’ Thus, a B-brain could act like a manager who has no special expertise about how to do any particular job—but still can give ‘general’ guidance like these.
If A’s descriptions seem too vague, B tells it to use more specific details.
If A is buried in too much detail, B suggests more abstract descriptions.
If what A is doing is taking too long, B tells it try some other technique.
How could a B-Brain acquire such skills? Some could be built into it from the start, but it should also be able to learn new techniques. To do this, a B-Brain itself may need help, which in turn could come from yet another level. Then while the B-Brain deals with its A-Brain world, that ‘C-Brain’ in turn will supervise B.
Student: How many levels does a person need? Do we have dozens or hundreds of them?
In Chapter §5 we’ll describe a model of mind whose resources are organized into of six different levels of processes. Here is an outline of what these might be: It begins with a set of instinctive reactions with which we are equipped with from birth. Then we become able to reason, imagine, and plan ahead, by developing ways to do what we call deliberative thinking. Yet later we develop ways to do “reflective thinking” about our own thoughts.—and still later we learn ways to self-reflect about why and how we could think about such things. Finally we start to think self-consciously about whether we ought to have done those things. Here is how that scheme might apply to Joan’s thoughts about that street-crossing scene:
What caused Joan to turn toward that sound? [Instinctive reactions.] How did she know that it might be a car? [Learned Reaction] What resources were used to make her decision? [Deliberation.] How did she choose how to make her decisions? [Reflection] Why did she think of herself as making that choice? [Self-reflection.] Did her actions live up to her principles? [Self-Conscious Reflection.] Of course, this is oversimplified. Such levels can never be clearly defined—because, at least in later life, each of those types of processes may use resources at other levels of thought. However, this framework will help us to start to discuss the kinds of resources that adults use—and some ways that these might be organized.
Student: Why should there be any ‘levels’ at all—instead of just one large, cross-connected cloud of resources?
Our general argument for this is based on the idea that, to evolve complex systems that still are efficient, every process of evolution must find a compromise between these two alternatives:
If a system’s parts have too few interconnections, then its abilities will be limited.
But if there are too many connections, then each change will disrupt too many processes.
How to achieve a good balance of these? A system could start with clearly distinctive parts (for example, with more-or-less separate layers) and then proceed to make connections.
Embryologist: In its embryonic development, a typical structure in the brain starts out with more or less definite layers or levels like those in your A, B, C diagrams. But then, various groups of cells grow bundles of fibers that extend across those boundaries to many other quite distant places.
Or, the system could begin with too many connections and then proceed to remove some of them. Indeed, this also happened to us: during the eons through which our brains evolved, our ancestors had to adapt to thousands of different environments—and, every time this happened to us, some features that formerly had been ‘good’ now came to function as serious ‘bugs’—and we had to evolve corrections for them.
Embryologist: Indeed, it turns out that more than half of those cells proceed to die as soon as they’ve reached their targets. These massacres appear to be a series of ‘post-editing’ stages in which various kinds of ‘bugs’ get corrected.
This reflects a basic constraint on evolution: it is dangerous to make changes to the older parts of an animal, because many parts that later evolved depend on how the older ones work. Consequently, at every new
