Flyus goldbergus

[From Rick Marken (950525.1215)]

Well. I was going to let this go but I just can't.

Bruce Abbott (950525.1100 EST) --

Ever wondered how a fly lands on the ceiling? If the optical signals
indicating a looming surface come from the upper portion of the eyes the fly
begins to extend its legs while increasing its angle of attack. The
forelegs make contact with the ceiling and the forward momentum gets
converted to rotational momentum, pivoting the fly's body around the contact
point, bringing the second set of legs into contact with the ceiling and
shutting down the flight motor. The legs are then adjusted to bring the
body level and the hind legs in contact with the ceiling, all accomplished
by means of a small set of perceptual control systems.

This is a very strange statement. You have described a sequence of causes and

optical signals from upper portion of eye-->leg extension & increasing angle
of attack--> foreleg contact-->rotational momentum-->pivoting around
contact--> second set of legs in contact--> shut down flight motor.

Then you say "...all accomplished by means of a small set of perceptual
control systems" as though it should be obvious from you description that
perceptual control is involved. But you never say what variables the fly
is controlling or what means it uses to control those variables.

You describe the mechanism of fly landing as though it were a Rube Goldberg
device rather than perceptual control system. Here is the analogous Rube
Goldberg device for fly swatting:

optical signals from fly--> picture on TV tube--> child watching TV with
fly swatter in lap stands up in horror --> contact between fly swatter and
floor --> Mom rotating at the hip to pick it up-->pivoting of fly swatter
as Mom picks it up-->swatter hitting ceiling-->shut down of fly's flight

The only hint of a controlled variable in your description of a fly landing
on the ceiling is when "legs are then adjusted to bring the body level"
suggesting that a perceptual representaion of body level is controlled.

There is more to perceptual control theory than just believing in it.