[From Bill Powers (2003.07.07.1100 MDT)]
For those who are worrying about the dwindling list, there are now 128
subscribers, two of them concealed. 96 of them are in the USA. At least one
subscriber is a newsnet list.
I think the most we ever had was about 145. Some listings are so old that I
seriously doubt their validity.
I have finally understood where Marc Abrams is coming from. He has got into
the literature of superreductionists, people who study calcium channels,
intracellular signaling, and that sort of thing. I have no word of
criticism for such work, but I do have cautions for anyone who thinks this
is the "real" picture of human organization. It tells us no more about
human organization than grinding up a radio and doing a chemical. analysis
of it would tell us about amplifiers, automatic gain control, tuned
circuits, or loudspeakers. It might tell us what these things are made of,
but it would not tell us the organization that makes them function as they do.
Nature is organized at many levels, even non-living nature. There are laws
that apply at each level, but the laws of one level do not reveal the laws
of the next level up (or down). You can understand how transistors work,
but to understand how a radio works you have to know how the transistors
are connected to each other and to passive components of the circuit. You
can't get that information from looking at a transistor, or a hundred
transistors. It is the organization of the circuit that makes it into a
radio. The same parts, differently organized, might make a metal detector
or an audio signal generator. Going the other way, the physical and
chemical properties of any one component represent emergent laws that grow
out of the properties of quarks and other fundamental particles. You would
have to know how the quarks are organized in order to find the laws at the
level of chemical reactions.
The level of organization represented by PCT is to cell chemistry as the
operation of a radio is to the holes and electrons in silicon, the atomic
matrix in copper, the laws of electromagnetism in an inductor, At an
intermediate level of analyzing the radio, we have components like
transistors, capacitors, inductors, resistors, and insulators, which can be
further analyzed into the detailed physics and chemistry of matter. At an
intermediate level in PCT, we have neurons, neural signals, muscle fibers,
hormones, and secretions, which can be further analyzed into underlying
biochemical and cell properties.
A neural comparator, for example, can be as simple as a neuron which
receives impulses that excite it to fire at the same time it receives, from
a different input connection, impulses that suppress the firing rate. The
net firing rate of the neuron is proportional to the difference between the
total amounts of excitation and inhibition. The net effect drops just to
zero when excitation equals inhibition. The firing rate thus represents the
difference between the excitatory and inhibitory inputs in terms of the
rates at which impulses reach the neuron. An analysis of an artificial
control system at the same level would say that a silicon comparator is a
transistor (or integrated circuit) with one input where incoming signals
act positively to increase the rate at which electrons pass through the
transistor, and another input where incoming signals act negatively
to decrease that rate. Thus the rate at which electrons are emitted from
the transistor represents the difference between the positive and negative
input effects, the function that a magnitude comparator has to carry out.
A chemical comparator can be made with allosteric enzymes (and other ways).
I'll skip the details, though they are known.
The neural and electronic circuits perform the function of magnitude
comparison, reporting a match as zero ouput and a mismatch as an output
signal of a particular magnitude. In both cases, a pair of such devices
would be needed to report mismatches of both signs.
In both cases, the operation of comparison can be further analyzed into
more detailed phenomena. An electronic comparator might be made of a pair
of field-effect transistors. In a field-effect transistor (there are
several kinds), we have a voltage applied to an insulated electrode,
setting up an electric field that either repels electrons from entering the
gate region, or attracts them into the gate region. A positive voltage on
the drain (collector) sweeps up all electrons that get into the gate
reqion. These processes can be analyzed further into states of excitation
of the electrons at the quantum level, and processes at that level can be
analyzed into phenomena of quantum chromodynamics. Of course as we pass to
each lower and more detailed level of analysis, we lose the ability to
predict phenomena at the higher level, because we lose the organization of
relationships among different elements at the higher level. At the ;eve;
opf transistors, analyzing a field-effect transistor does not tell us that
there are two transistors connected in a common-source configuration. At
the level of quantum effects, there is no such thing as a transistor.
In the nervous system, the comparator can be analyzed in terms of
neurotransmitters that alter the ionic concentrations inside the receiving
neuron, changing the electrical potential (voltage) at the axon hillock.
This basic potential is maintain by continuously operating calcium pumps,
and is modified by the effects of incoming neurotransmitters, both
excitatory and inhibitory. When the potential at the axon hillock exceeds a
specific threshold, there is an electrical breakdown, which triggers a
breakdown in adjoining parts of the axon, and sends a wave of breakdown
traveling along the axon at anywhere from 1 to 100+ meters per second,
depending on the axon diameter. All the breakdowns are quickly restored by
the calcium pumps, but another impulse can't be generated until the
potential has risen enough, which takes a millisecond or so. These
processes can be analyzed further into the properties of organic molecules
which fold and unfold to open and close pores and even act like tiny motors
carrying molecules from one place to another, and from there we can go even
further into quantum mechanics. As we pass downward from level to level, we
lose the laws that operated at each previous level and begin to study new
laws, all of which are basically laws of organization.
Obviously, one could never learn how a radio works by studying flows of
electrons through transistors and other physical components. Even to start
to understand what is going on inside a radio, we have to get some idea of
what each part of the total system _does_. For example we will find
capacitors that store electrical charges, and inductors that generate
magnetic fields when electrons flow through them. In certain places we will
find a capacitor with its leads connected across the ends of an inductor,
so we have electrons being stored in the capacitor but quickly flowing
through the inductor as the capacitor discharges. We will also find that
current flow through the inductor generates a magnetic field which quickly
collapses, and in collapsing drives electrons out of the inductor -- and
into the capacitor. Clearly there is some special relationship here between
these two components that can't be understood by studying either one by
itself. What they form together, as some here will know and some won't, is
a "tank circuit," and this tank circuit can be used to tune in specific
frequencies of incoming electromagnetic radiation. When you turn the tuning
knob of a radio, you are changing the characteristics of a variable
capacitor connected across an inductor, and so changing the natural
frequency of a tank circuit (in a "local oscillator" circuit).
The rest of the radio is similarly composed of components interacting with
each other to perform specific functions: gain control, intermediate
frequency amplification, audio rectification, audio amplification, and
conversion of electrical signals into audible sounds. None of these
functions is visible in any one component; they are carried out by
components acting together according to their individual properties. Each
function generally uses components like those used to carry out other
functions; it is the organization more than the component that determines
what is done.
Now apply this to the neural control system. A network of neurons can
create an output neural signal having a frequency that is proportional to a
weighted sum of a set of input neural signal frequencies. This function can
convert a set of perceptual signals into a new signal representing a
property of the whole set -- a new and more general perception. That signal
can enter a comparator along with a reference signal to produce a signal
indicating the difference in frequencies between perception and reference,
and the resulting difference signal or error signal can be used to operate
actuators, muscles, so as to reduce the difference between perception and
reference. The result of this whole set of processes all being connected
(in the correct way) into a closed causal loop is the phenomenon we call
"control". Control is not a property of any one component in this
organization. It is a property of the whole organization. It can't be found
by examining any part in greater detail. In fact if we drop to the level of
calcium channels and intracellular signaling, we will completely lose sight
of what this whole assemblage of components _does_, which is to control its
own inputs and keep them in a match with the reference signal it is receiving.
In trying to understand human organization. we must understand each level
of organization before we can begin to understand the level below. Of
course as our picture of underlying processes becomes clearer, we can
profitably modify our concept of the higher level, too. If we try to
penetrate too many levels in one jump, we will become lost in
incomprehensible details -- just look at the reports in Nature or Science,
where we are snowed under by blizzards of unconnected facts, or facts with
connections only over a very tiny fraction of the whole picture. That will
basically get us nowhere, and people have been complaining about this as
long as I've been reading the literature.
A last note. People use the word control in different ways, which include
the meanings of "to limit," " to influence or affect," and "to determine."
In PCT it means none of those, so we would never say, for example, that
opening a calcium channel controls the flow of calcium ions. If something
is controlled, under the PCT definition, then any disturbance tending to
alter it will be opposed by a change in the action of the control system
that is affecting it. To do this, a closed-loop system and not a
single-stage causal link is always required. A variable can't be controlled
under this meaning unless something senses its state, compares what it
senses against some reference standard, and acts on the basis of any
discrepancy to change its action on the controlled variable in the right
direction for negative feedback.
There is nothing wrong with studying the details, either of electronic
circuits or boplogical systems. But true understanding is not to be found
at any one level of analysis.
Best,
Bill P.