Egg retrieval

Marc Abrams (990401.2104) --

[From Bruce Abbott (990401.2015 EST)]

... If one views the "goal" of this
activity as rolling the egg back into the nest, then the apparent fact...

These are perceptions and reference levels _you_ ( or some researchers ) are
attributing to the goose. This is not a statement of what the _goose_ might
be controlling for. _Everything_ else that follows, comes from these
assertions.

Marc, there's a reason I put the quotes around "goal." I am referring to
the typical result of this action pattern, one which has obvious biological
significance (to us, not to the goose!). It is easy to imagine how a system
that typically produces this result might have been selected for over the
course of evolution.

Regards,

Bruce

from [ Marc Abrams (990402.1019) ]

Marc Abrams (990401.2104) --

[From Bruce Abbott (990401.2015 EST)]

... If one views the "goal" of this
activity as rolling the egg back into the nest, then the apparent fact...

Marc, there's a reason I put the quotes around "goal." I am referring to
the typical result of this action pattern, one which has obvious biological
significance (to us, not to the goose!). It is easy to imagine how a

system

that typically produces this result might have been selected for over the
course of evolution.

Bruce, I guess I have a difficult time believing that animal studies ( i.e..
the non human kind :slight_smile: ) can be used usefully in "behavioral" studies. I can
see ( barely :slight_smile: ) how certain biological sub systems _might_ be similar and
useful. I just think extending that to behavior is a stretch. Obviously I
could very well be wrong in that belief. I just don't know _how_ I would be
able to _know_ that.

Marc

[From Bruce Abbott (980402.1050 EST)]

Rick Marken (990401.0940) --

I looked at the Quicktime. This is no fixed action pattern!
What it looks like to me is control of pressure against the
inside of the bill.

A fixed action pattern is a stereotyped _series_ of acts. You are focusing
on only one component -- the movement of the bill toward the goose's body.
Missing are the acts of moving to bill to a position on the side of the egg
opposite the goose, standing when the egg is near the body, tucking the egg
under the body, and sitting on it.

When the egg is removed (bringing the
perception of pressure instantly to zero) the goose moves
the bill (in what appears to be an accelerated rate) in the
direction that _would_ increase the pressure on the inside of
the bill if the egg were still there. Neck movement seems to be
the output variable of a pressure control system. This system
is organized so that movements of the neck towards the body
are used to _increase_ pressure perception and movements away
are used to _decrease_ pressure perception. This would be the
right way to have the sign of the error (difference between actual
and reference pressure) affect the output variable (direction of
next movement) to have negative feedback (control of pressure).

Yes, that _could_ be.

The apparent "exponential runaway" when the egg is removed
is exactly what you would expect from a system with an integrating
output controlling for a non-zero perception of pressure by
pulling back on an object that is no longer there. The system's
(integrating) output increases exponentially, driven by a constant,
non-zero error.

You see "exponential runaway" because that's what you expect to see in such
a control system. But there are at least two alternative possibilities you
have not considered. First, speed of retraction may have increased simply
because the system was "unloaded" -- no heavy egg to push. Second, speed of
retraction may have increased because the side-to-side balancing movements
usually required to keep the egg moving on its proper course are not
required when the egg is removed. The bill therefore has a more direct
route to follow. The balancing movements themselves are control actions, of
course, that compensate for deviations of the egg's path toward the goose.

Of course, more tests are needed to prove that
pressure is controlled.

Or to show that it isn't.

But it's pretty clear from the Quicktime
that this "egg-retrieval" behavior is not necessarily (indeed, not
likely to be) a "fixed action pattern".

Again, you're only looking at one part of the "fixed action pattern." This
is like focusing on one solid-colored square of a plaid pattern and
concluding that there is no pattern there, only one solid color.

Regards,

Bruce