VOR feedforward

[From Rick Marken (931116.2030)]

Gary Cziko (931116.2200 GMT) --

Don't forget about the vestibulo-ocular reflex. Looks like we need
feedforward there--even Bill Powers says so.

Don't know much about the VOR (sung to the strians of Sam Cooke).
Apparently VOR refers to the behavior of my eyeballs when I turn
my head back and forth with my eyes closed. Is that it? When I do
this my eyes seem to remain pointed forward. It seems to me that
some perceptions are involved -- even when my eyes are closed. But
I'm willing to believe that there is an open loop component to the
VOR. I guess I would be impressed if the "reflex" were as accurate
when the eyes are closed as when they are open. If eye movements
are equally accurate in both cases, and if there were evidence that
no other perecption were being controlled in the eye closed case (ie.
the eye movements are really being generated "open loop") then it
seems that the muscle contractions that produce these movements are
indeed being produced by a PRECISELY CALIBRATED feedforward signal.
This would be most impressive to me and a strong demonstration of
the involvement of what I would consider a REAL feedforward process.

What I think is more likely is that the open-loop component of the
VOR (assuming that it exists) is an UNCALIBRATED ballistic push
in the "right" direction (the direction that will keep the eyes
pointing straight ahead). This feedforward push occurs in the
context of a closed loop that is controlling a perception of
something like felt eye position (it seems to me that I can feel
something about the position of my eyes when I turn my head).

So my guess (and I could be wrong -- I need more data) is that
the open loop component of the VOR is like the random tumble
of e. coli. The tumble, like the force of the ballistic push in
the VOR, is "uncalibrated" (completely random in e. coli; rel-
atively imprecise in the VOR) but it "gets the output rolling"
with the effects of that output being trimmed up almost immediately
by the closed loop process of which it is a part.

Could you describe some of the evidence that the VOR is open
loop. How accurate is the VOR? Have there been measurments made
of the neural impulses that produce the muscle contractions that
produce the initial eye movement? Is the magnitude of those
impulses proportional precisely to the amount of contraction
(and, hence, movement) that SHOULD occur (given the amount of
head rotation)?

I agree that the VOR might be a very nice example of feedforward
control. So let's look at the data.

Best

Rick