Игорь Волков – Hardware and software of the brain (страница 6)

Another important detail. The human brain may be described as a finite-state automaton but how to reconcile this with the highly dynamic nature of human behavior? The solution turns out to be simple. In many cases, dynamics is a cyclic activity. For a computer, this is triggered by some event, then maintained by an algorithm. In the brain, also some control signal is involved, but it isn't a short pulse. Instead, it is a long strobe and activity continues while this strobe remains active. Moreover, recall that nervous signals are digital-analog so the strobe may change its amplitude and regulate the strength of output actions or their frequency. Continuing the example with walking, humans don't think about single steps. They are generated by low-level servo control. The next step is automatically launched when the heel hits ground at the end of the previous one. Dynamism of walking is maintained by spinal gear while central control sends just 2 static commands: walk or stop.

After this introduction, let's try and describe human software in details. For a computer, there is a hierarchy of programming languages. The first one was The Language Of Assembler or just Assembler which consists of instructions that are immediately supported by the processor hardware of the computer in question. The next level contains languages of system programming. The most known is C that was conceived as a universal Assembler which should work on different machines. Further up will be application languages to write software for end users and particular application domains. Typically, the languages of lower levels are used to create a programming tool for the next level upwards. That is, when you use a single operator of an application language, it employs several elementary commands and instructions of lower levels. As a result, very complicated and clever programs are composed of a few very simple instructions. Hence, we need to seek for such most elementary internal actions supported by brain hardware.

The most obvious are memory read/write operations. Humans can remember separate images and later recall them. In addition, they can remember associations between 2 images. Then, when the first is presented, heteroassociative memory returns the second.

The next function is evaluation. The limbic system receives input from different sensory channels and generates a positive or negative drive depending on how the current situation compares to expectations. These drives work as start/stop instructions which are important for asynchronous architecture.

Now add various methods of data processing implemented in structured multilayered neural nets and you will get a computer with a decent set of instructions which may be used so as to develop sophisticated programs.

System software and applications

Newborn humans are virtually helpless. Can't walk, even stand. Unable for coordinated actions. Moreover, they don't know elementary actions themselves. On the other hand, it is well known that if a human hadn't learned any language at early age, he can't do it as an adult. Seemingly, human learning is arranged similarly to installation of computer software. An operating system comes at the beginning. Accordingly, you need to learn some basic skills first. Then, the rest will be added on this foundation.

Meanwhile the difference is substantial too. A computer comes with a ready instruction set and electronic circuits for algorithmic processing. Creation of human system software begins with creation of a discrete processor on the basis of the analog neurosubstrate. This firmware operates in accordance with principles outlined in Formal neurocomputer.

The rest of system software constitutes what is known as "culture". It includes such elements as habits to wash your face or clean your teeth, preferred clothes and dishes, usual time when you go to bed and wake up, etc. The most characteristic feature of a culture is its language. As in computers, system software divides into that which supports individual behavior and that for communication and cooperation (networking). Each nation has its unique traditions of interaction.

Finally, when a person has more or less remembered these components, it's time for professional education. That is, installation of application software begins. Computers have many programming languages. Each was developed for a certain class of applications. In humans, a natural language serves as a universal one. Nevertheless, each profession develops its own dialect with special terminology and even a specific style of thinking.

Complete theory of natural language

When we hear "theory" during a discussion of human language, the first idea is grammar. Syntax, punctuation, word spelling, etc. Meanwhile this is only a superficial wrapping. There is also at least semantics which is more important than purely formal grammar, but you won't find a comprehensive course on this discipline. On the other hand, when professional linguists discuss language usage, there is one problem. How to tell a correct construct from incorrect one? For a student, it is simple. Just open a textbook, but how to decide it for a professor who writes these textbooks? It turns out that they can't suggest anything better than intuitive "well-formedness".

Human language is a part of a live computational system. For a neurocomputer, the problem of "well-formedness" becomes quite practical. It may be resolved on the basis of computational efficiency, reliability, informational capacity, and so on. Let's try and formulate the structure of natural language in this aspect. We will keep in mind English because it is a lingua franca and also its fixed word order makes it easy for parsing. Nevertheless, usually speculation should be applicable to other human languages as well.

What is natural language?

Human language is a communication channel for a live computing system. It is very different from common computers. On one hand, knowledge of this system as a whole is very useful for understanding of how this language works. On the other, even if we don't know its inner details, we still can access its functions via the language interface. Existing computers are famous for being universal. On one hand, the human brain is universal too, on the other it is extremely specialized. In fact, it has just the single task – homeostasis. Existence is the ultimate goal of this automatic control system. Variability is needed to adapt to a wide range of living conditions. The whole complexity of human behavior may be logically derived from this root. The overall brain may be represented as 2 regulators – the internal and external one. The first looks inside, the other – outside, but they do the same – maintain the reality in accord with some ideal image. If your blood contains little nutrients, eat something. If your shoes became old and don't protect from water, throw them out and buy new ones. To evaluate the disbalance, we need 2 images – an ideal and real one. Our sensory organs permanently update the second. We don't know exact details of its internal representation but can communicate it via the language channel with any precision required.

Assignment

In computers, we have many different languages, each for a specific purpose. Instead, humans use one language in all of these cases. You can even tell some words which directly affect internal organs or the state of the brain itself. This is an assignment of Assembler – the language for hardware programming. You can code an algorithm like with Basic, formulate a question, that is a query to a database like with SQL, or use it for communication as HTML.

Classical hierarchy of language structure

This is widely known as

Lexicon – Syntax – Semantics – Pragmatics.

The first level contains various words. All of them are divided into several different parts of speech – nouns, adjectives, adverbs, … Syntax is a set of rules which define how these words group into noun phrases, verb phrases, and other constructs. They further group into clauses and sentences that represent elementary complete ideas. The flow of the text represents the flow of ideas in human mind. Note that syntax rules are formulated in grammatical categories. They are meaningless, used only to link words with each other. Some meaning emerges on the next, semantical level when the syntax structure is considered together with concrete words within it. Nevertheless, this meaning is still incomplete. It is called "direct" one. On the last, pragmatical level, context is added and we receive "indirect", derived meaning of the text. Context also plays the crucial role in disambiguation.

This scheme looks perfect, but is it really workable? Grammar was added later in human history. It is mainly associated with written language. Like any theory, it only partially fits the reality of live human communication. A typical cycle for learning a foreign language is studying a grammar textbook, passing the exam, then forgetting it all and taking a practical course of business English. Why such discrepancy?