"completely" closed loop = ?

CSGnet Archive CSG1992
1

From Greg Williams (920323)

Rick Marken (920323 8:30)

Which brings me back to my question from a couple days ago: how do
researchers know about the open-loop organization of the cockroach
escape response?

I've learned my lesson regarding posting synopses of data. You'll have to read
it yourself. I suggest that you begin with J.M. Camhi, NEUROETHOLOGY, 1984.

I just can't understand how any "behavior" that consistently
achieves some result (escape) could be completely open loop (unless it were
always performed in the same environment, from the same orientation, with the
same motor charateristics, etc.). The achievment of consistent results
in a variable environment is control, by definition. And the only way
we know know how to make systems that control is to build systems that
sense and have negative feedback effects on the result that is to be
produced consistently.

I'm not sure I know what you intend by "completely open loop," but I think
that the cockroach's controlling for perceiving no-air-puff can be achieved
quite reliably via the following control mechanism: air-puff coming from a
certain direction affects sensory hairs in particular ways, resulting in
precalculated patterns of stimulation to leg muscles, usually (but NOT ALWAYS,
since the "calibrated" action is NOT protected against disturbances) moving
the bug in a direction away from the air-puff source. I suspect that highly
consistent (even in the face of disturbances), "completely closed loop" (?)
escape actions would be less economical in this situation, and/or might be
slower than precalculated, calibrated action. Ongoing, fine control of the
bug's trajectory simply isn't necessary to (almost always) escape. Still,
there is a closed loop here, even if (again, guessing at your meaning) it
isn't "complete." In a sense, it IS complete, as the loop encompasses the
ballistic movement to get "away" -- the bug (generally) does get away, thus
achieving control. BUT ONGOING CONTINUOUS CONTROL ISN'T REQUIRED. One might
say that the control is continuous, since the sensors are continually
receiving information about air-puffs, but I claim it isn't continuous,
because no use is made of that information except to "aim" and "fire" each
"triggered" ballistic action following an air-puff.

Greg

2

[From Chris Malcolm]

Rick Marken (920323 8:30) writes:

I just can't understand how any "behavior" that consistently
achieves some result (escape) could be completely open loop (unless it were
always performed in the same environment, from the same orientation, with the
same motor charateristics, etc.). The achievment of consistent results
in a variable environment is control, by definition.

This is a common misconception. It is possible for behaviour to be
adaptive in the sense of changing appropriately in response to the
environment without even involving any sensors, let alone controlled
variables. There are two ways it can be done. The first is to use
unstable motor behaviour where the environment selects the appropriate
behaviour. The second is where the appropriate behaviour concerns part
of the environment rather than the creature, e.g., putting something
into a hole. This can be done by using fixed predetermined behaviour on
the part of the creature to determine only part of the behaviour of the
item in question, and letting the local environment also affect it, with
the net result that fixed behaviour on the part of the creature results
in goal-seeking behaviour on the part of the item in question (the thing
which is being put in the hole, for example).

These two cases seem to many people to be so counter-intuitively absurd
that they cannot believe it possible, but as the history of science has
so often shown, failure of our human imaginations is not a reliable guide
to impossibility in our universe!

In order to convince students of this I have built a couple of simple
robot systems which demonstrate these two cases. Look Ma, adaptive
behaviour with no sensors!

After a suitable pause for speculative ingenuity I will describe these
systems.

Only two ways? Well, I have only been able to think of two ways. I hope
some of you will be able to think of some more!