ROSS ASHBY - The Cybernetic Brain - page 124

subassemblies appropriate to some adaptive task without the patterns of split-
ting having to be hard wired in advance. DAMS would thus turn itself into
a sparsely connected system that could accumulate adaptations to differing
stimuli in a finite time (without disturbing adaptive patterns that had already
been established within it).
At the hardware level, DAMS was an assemblage of electronic valves, as
in a multihomeostat setup, but now linked not by simple wiring but by neon
lamps. The key property of these lamps was that below some threshold volt-
age they were inert and nonconducting, so that they in fact isolated the valves
that they stood between. Above that threshold however, they flashed on and
became conducting, actively joining the same valves, putting the valves in
communication with one another. According to the state of the neons, then,
parts of DAMS would be isolated from other parts by nonconducting neons,
“walls of constancy,” as Ashby put it (1952, 173), and those parts could adapt
independently of one another at a reasonable, rather than hyperastronomical,
speed.
Not to leave the reader in undue suspense, I can say now that DAMS never
worked as Ashby had hoped, and some trace of this failure is evident in the
much-revised second edition of Design for a Brain . There Ashby presents it
as a rigorous deduction from the phenomenon of cumulative adaptation to
different stimuli, P 1 , P 2 , and so on, that the step mechanisms (uniselectors in
the homeostat, neon tubes in DAMS) “ must be divisible into non-overlapping
sets, that the reactions to P 1 and P 2 must each be due to their particular sets,
and that the presentation of the problem (i.e., the value of P ) must deter-
mine which set is to be brought into functional connexion, the remainder
being left in functional isolation” (1960, 143). One can see how this solves
the problem of accumulating adaptations, but how is it to be achieved? At
this point, Ashby wheels on his deus ex machina, a “gating mechanism,” Γ,
shown in figure 4.9. This picks up the state of the environmental stimulus P
via the reaction R of the organism to it and switches in the appropriate bank
of uniselectors, neons, or whatever that the essential variables (the dial on
the right) can trigger, if necessary, to preserve the equilibrium of the system.
But then the reader is left hanging: What is the go of this gating mechanism?
How does it do its job? Almost at the end of the topic, eighty-four pages later,
Ashby acknowledges that “it was shown that . . . a certain gating-mechanism
was necessary; but nothing was said about how the organism should acquire
one” (1960, 227). Two pages later, Ashby fills in this silence, after a fashion
(1960, 229-30): “The biologist, of course, can answer the question at once;
for the work of the last century . . . has demonstrated that natural, Darwinian,