History of Ideas (was Re: Latash, 2010: "Motor Control Theories and Their Applications")

[Martin Taylor 2013.]

Mackay's paper is targeted at an explanation of the perception that

we have free will despite being physical beings constrained by
physical laws. The first half, however, is devoted to building a
background for his argument. That background is the surprise. In it, he describes what appears to
be exactly the Latash et al. model so far as I understand both
Mackay and Latash et al., but he uses it only as the lowest level
component in a hierarchic control structure. Mackay describes the
lowest two levels and says effectively “and so on”, each level
providing reference values for the inputs from lower levels. It is
pure PCT, despite that the paper title seems to say otherwise:
“Cerebral Organization and the Conscious Control of Action”. The
diagrams and text make clear that it is input that is controlled. He
explicitly rejects the concept of predetermined cancellation of
error-producing disturbances, and the specification of output
So far as I know, Mackay never developed this idea. At least, I
don’t think he ever spoke to me about it during my Sabattical year
at Keele. The main point of the paper was to deduce a logical
consequence of the structure. He says that if the hierarchic
closed-loop structure exists, then “it is impossible in principle to
deduce, from the prior state of the world including the agent’s
brain, a prediction of his choice on which agent and observer would
be right to agree. … In this sense typical human choices would be
‘logically indeterminate’ even if the flow system that mediated them
were physically determinate.” I imagine that it was only in this context that Mackay saw the
hierarchic control structure as important. To me, that puts Mackay
among those who had the background and opportunity to see the power
of PCT, but who missed Bill Powers’ insight of genius, that it
really matters. Be that as it may, I find it interesting in the
present context that back in 1955 Mackay put the Latash structure in
the context of a explicit two-level control system in which the
upper level provides the reference value for the lower level. Reference: Mckay, D.M., Cerebral Organization and the Conscious
Control of Action, Pontificiae Academiae Scientiarum Scripta Varia,
30, 1955, 627-663.


In 1966-7 I had a Sabbatical at Keele University in England at the
invitation of Donald Mackay. Today, I came across an old paper
reprint of a 1955 presentation by him at a Symposium apparently on
the cerebral basis of consciousness. He must have given it to me
in person along with others of his reprints. I haven’t seen this
one for ages, and quite probably have never read it before now. At
least I don’t remember having seen it. As you will see, this is
relevant to the Latash thread.

[From Rick Marken (2013.12.29.1600)]

    > Bruce Abbott (2013.28.1745 EST)--
      >BA:  I've been doing some on-line reading of the

literature on the equilibrium point (EP) model and can see why
Latash et al. would not be aware of any connection of their
model with PCT.

    RM: It's not that they are "not aware" of a connection; they

explicitly reject a connection because they reject control


BA: In fact, I’ve found it difficult to understand their
model, given the descriptions I’ve read of it. Thus far I have
not seen a discussion of how the “commands” of the system are
derived; it could very well be an open-loop system at that
level, or maybe not.

    RM: I'm pretty sure it's an open loop model. Their "commands"

are not like reference signals because they not specifications
for input. Rather, they are commands for output – they cause
the tensions in the muscles (outputs) that determine the
equilibrium point of the limbs to which the muscles are