VOR as Compensation

[from Gary Cziko 930903.2028 UTC]

Bill Powers (930901.0830 MDT) said:

A compensating system of this kind would pass several parts of the
Test. The controlled variable would indeed be stabilized against
disturbances, and the actions of the system would be affecting
the controlled variable in a way equal and opposite to the
effects of the disturbance. However, when you block all ways for
the supposed control system to sense the controlled variable
itself, control would continue instead of being interrupted. The
effects of the disturbance on the controlled variable would
continue to be resisted by variations in the system's output.
This would prove that the system is NOT a control system in the
PCT sense, but what I term a compensating system.

I sent this post to my friend Tom Anastasio (who does work on the
vestibulo-ocular reflex (VOR) in goldfish) along with some questions. Here
is the interaction with >> = me and > = Anastasio:

I think I must have asked you this before, but I can't remember if the VOR
works in the dark.

You did and it does.

If so, that would indicate pretty clearly it is an
open-loop compensatory system.

It is.

But if it is not as accurate in the dark,
then perhaps this would indicate that retinal slippage is needed to keep
the system tuned up properly.

Retinal slip is needed to keep the VOR tuned-up in the long-term, as you
said above. It also helps in real time eye position stabilization, but
mostly at lower frequencies. At higher frequencies, the optokineitc system
(the control system that minimizes retinal slip) does not work well at all,
and visual image stabilization is acheived primarily by the VOR working
alone. Note that frequencies at which optokinetic system works poorly, and
VOR works well, are behaviorally very important since most head rotations
occur at those higher frequencies.

So, does the VOR not pass the test for being an open-loop, compensatory
system? And if so, are there any other animal behaviors which also pass
the the test for compensating behavior?--Gary

P.S. In spite of the obvious open-loop behavior of the VOR, why do I find
myself wanting to somehow attach a rubber band to someone's eye and give
some disturbing tugs during a head movement to see if the VOR is able to
resist the disturbance to retinal stabilization (it should not if it is


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