[From Bruce Abbott (2017.02.25.1250 EST)]

Rick Marken and I have been offering different definitions of Qi.

Rick prefers to think of Qi as an observer’s view of what is being perceived by a control system. If the perception p is being computed from two environmental variables v1 and v2 by, say, multiplying them together, then Qi = v1 X v2.

I prefer to think of Qi as an environmental input quantity. (That is, after all, what “Qi” is supposed to stand for.) If there are two variables that serve as inputs to the input function, then I would represent them as, say, Qi1 and Qi2. If these are being multiplied together to yield p, then p = Qi1 X Qi2.

Below is a diagram showing each version, mine on the left and Rick’s on the right:

Note that, in Rick’s version, both p and Qi are equal to the product of v1 and v2. Therefore Qi = p, save for a conversion factor to rescale p from the units in which the environmental variables v1 and v2 are expressed to the units in which p is expressed (e.g., neural impulses/second). Rick, if I understand him correctly, says that Qi is the observer’s perception of the controlled variable, and therefore does not exist unless there is an observer. But this leads to the problem that Qi is no longer an input quantity (located in the environment) but rather another p, located in the observer. So would it be better to identify the little circle in Rick’s system with another p? And how should it be computed? To compute this p, wouldn’t we need to know the *observer’s* input function, rather than the control system’s?

This whole problem can be avoided by assuming that the quantities entering the input function are real environmental variables like light intensities or water temperatures rather than an observer’s perceptions of them. We eliminate the observer from our description of how control systems work (they appear to work just as well when not being observed) and we don’t have to deal with silly philosophical questions similar to the one asking, if a tree falls in the woods and there is nobody there to hear it, is there a sound? (The answer depends on how one defines “sound.”)

Put THAT in your pipe and smoke it!

Bruce