[Martin Taylor 2010.04.18.15.31]
[From Martin Lewitt (2010.04.17.1525 MDT)]
I wonder if PCT is falsifiable.
I suppose it depends on what you mean by "PCT". The phrase "Perceptual Control Theory" can be, and is, used in quite a few different ways.
At one extreme is the Rick Marken usage, in which "PCT" means precisely the 11-level purely hierarchic organization of scalar control units described by Bill Powers, along with the assertion that all behaviour is the control of perception. This version would be falsified if it were to be determined that the control structure is not strictly a pure hierarchy of scalar control units, or if one even one occasion some action could be determined not to be the output of a functioning control system.
Bill P has a slightly less rigid usage, since he frequently mentions that the nature and ordering of the levels of the hierarchy are not cast in stone, and in his modelling he sometimes inverts the ordering of some levels. But Bill's usage still asserts a strict hierarchy of scalar control systems, and would be falsified if it could be shown that even one feedback loop existed within a level (as would be the case, for example, in a flip-flop decision circuit at the category level -- a quite plausible possibility). Both Rick's and Bill's versions would be falsified if it were ever determined that some controlled perception was not scalar (the analogy to the studies of perception when I was in school would be to "integrable" and "non-integrable" perceptual dimensions).
I try to use the term "HPCT" or "Hierarchic PCT" to refer to the theory when it includes a strictly hierarchic organization of scalar control systems (and I suppose I would continue to do so if the control units were hypothesized to control vector perceptions rather than scalars). In my usage, "PCT" is more general. For me, it would still be PCT if it were found that control systems existed that sensed and controlled the actions of other control systems within the same structure, such as altering their gain or changing the parameters of their sensory input functions. Such "interior" control systems cannot exist in HPCT, and the discovery of one would falsify HPCT. Likewise it would still be PCT if the value of one controlled perception influenced the value of another perception (controlled or uncontrolled). Such an interaction is disallowed in HPCT, at least in the pure version.
Going to the other extreme, at the most general level, PCT can be seen as a corollary of the thermodynamic law that entropy always increases to a maximum in a closed system, since the influence of the environment in reducing the Gibbs free energy of the environment-lifeform system is unavoidable. The structure of the lifeform can be sustained only by either isolating the structure from the environment (skin and shell) or by sensing and countering the environmental effects that would destroy the structure. This second possibility is exactly "PCT" in its most general usage. In this sense, PCT is falsifiable only by a falsification of the second law of thermodynamics.
Between the essentially unfalsifiable "general PCT" and the easily falsifiable HPCT, there is a range of possibility. For example, in some usage, does PCT claim _all_ behaviour is the output of actively functioning control system(s), or does it claim that _some_ behaviour is the effect of control, while other behaviour may be spontaneously generated, or may be intentionally output without any corresponding sensory input that must be brought near a reference value (that's two different variants, but they might be combined). The "all behaviour" version could be falsified if it could be shown that even one action was not intended to influence a controlled perception. The "some behaviour" version would be proven correct if even one action could be shown to have been performed so as to bring some perception closer to a desired value. Having proved that, the "some behaviour" variant would be unfalsifiable in the same sense that the claim "some days are sunny" is demonstrably true and is therefore unfalsifiable.
There's no value in going through all the different possible meanings of "PCT", at least not for determining whether PCT is falsifiable. If you want to test a theory, you have to specify what that theory claims. Once you have done that, you can assess whether it is falsifiable. But "PCT" is a moving target, and if you falsify one version, there are lots of others awaiting your arrows. It is much easier to assess the falsifiability of a version of PCT that makes a specific claim about the organization of control units than it is to assess the falsifiability of a version that just says there must be some organization without specifying what that organization might be.
So, is PCT falsifiable? Let me be perfectly clear: "Yes and No, and maybe".
Martin