What Is PCT Research?

[From Bruce Abbott (950530.1140 EST)]

One of the points to come out of the overly-extended discussion between Rick
Marken and me about insect research was Rick's definition of what
constitutes PCT research. According to Rick, PCT research is aimed toward
identifying in a given situation the controlled perceptual variables, by
systematically applying disturbances and noting whether these disturbances
are resisted (i.e., conducting the Test). I agree that this step is
essential, but I see it as only one phase of what I would define as PCT
research. In my view, research in which the closed-loop nature of the
system under study is explicitly recognized and studied as such would
qualify. Such studies might be aimed at identifying the controlled
variables OR at elucidating the specific structures involved and their
functions within the control system. The focus might be on a quantitative
analysis of receptor input functions, motor output functions, comparator
functions, and so on. When I encounter work like this in the literature I
think, hey, PCT stuff! I'm not sure that Rick (and Bill Powers) would
agree, given Rick's narrower definition.

Before we get into another heated debate over whether this or that research
is PCT research, I'd like this issue settled. If you prefer to hold to your
definition, then I'll simply change nomenclature and refer to the more
general approach to understanding control systems as "control systems"
research rather than PCT research.

An example of the kind of research I have in mind is Kittmann, R. (1991).
Gain control in the femur-tibia feedback system of the stick insect.
_Journal of Experimental Biology_, _157_, 503-522. (This is one of the three
journal articles I cited in an earlier post as an example of PCT research on
insect behavior.) The title is self-explanatory. The reported study
follows up on Kittmann's earlier work on the same system; in the current
paper he describes quantitative aspects of the system as studied under both
closed-loop and open-loop conditions. Kittmann notes the following in his
introduction:

    In proprioceptive feedback systems there is a lack of quantitative data
    concerning . . . changes in the characteristics of the system. The
    variation in gain -- the ratio between the output and the input of the
    system -- is particularly important, as it can change the characteristics
    of the system considerably. Low gains result in ineffective feedback
    responses, whereas high gains can induce instability, e.g., oscillation of
    the system. Therefore, to maintain effective feedback, gain must be
    carefully controlled.

Kittmann's preparation was as follows:

    Extracellular activity of the extensor tibiae motoneurones was recorded
    from the extensor nerve with 50 micrometer steel wires. Closed-loop
    experiments were performed under these conditions. For open-loop
    experiments, the fCO was mechanically stimulated as described by BAssler
    (1976); a pen motor with a pair of forceps connected to its acis was used
    to move the chordotonal apodeme, which was cut distally at the FT joint.

Now it seems to me that a study of the gain of the proprioceptive feedback
system and its variation under varying experimental conditions is a PCT
study. Is it? If not, please explain.

Regards,

Bruce

[From Bruce Abbott (950531.1215)]

Rick Marken (950530.1300) --

Bruce Abbott (950530.1140 EST)

Now it seems to me that a study of the gain of the proprioceptive feedback
system and its variation under varying experimental conditions is a PCT
study. Is it? If not, please explain.

This is a good question. I would say that such a study is a PCT study as
long as one had already identified the significant components of the
control loop - - in particular the controlled variable, perceptual signal,
reference signal, error signal and output variable.

Bill Powers, do you agree?

Regards,

Bruce