Where are reference signals and error signals?

[From Bill Powers (921202.1730)]

Audra Wenzlow (921202)--
John Gabriel (921202) --

The puzzle you are working on is the same one I went through in
developing the definitions of perceptions in the hierarchy. I expect
that Rick Marken will be along with a message similar to mine shortly.

Audra says:

For instance, in the rubber band experiment, I don't really care
where the knot is, only how far I perceive it to be from the
reference point. In other words, I am not controlling my
perception, but the difference between my perception and my
reference level.

When you describe it this way, it seems that the knot's position is the
controlled variable, while the position of the spot where you are
keeping the knot is the reference signal. This creates a puzzle, because
in the HPCT model reference signals pass downward from higher systems
into the comparators of lower systems, and don't come in through the
senses. Only perceptions originate in the senses. So is a reference
signal also a perceptual signal? This leads immediately to

I understand that how I see this error is also a perception, but
the distinction between "the perception of how far away my
perceptions are from my reference signal," and my perceptions
themselves should be made.

So now we also have error signals originating in the senses and becoming
perceptual signals. If you try to draw the control-system diagram so
that not only perceptions, but reference signals and error signals are
inputs from the environment, you will soon end up in a conceptual mess.

This is not a trivial problem; you are astute to have pursued it to this

Behind my answer to it lies a fundamental postulate of HPCT, which is
that the world we experience exists ONLY in perceptual signals. We do
not perceive error signals. We do not perceive reference signals. The
original reason for proposing the imagination connection was precisely
to provide a way to get the information in a downgoing reference signal,
which is not perceived, into the perceptual channels where all
perception takes place. Only in this way can we maintain consistency
with the postulate that all experience is of the perceptual signals, and
still explain how we sometimes -- I stress sometimes -- can know the
reference condition directly. And I believe that this postulate is
essential in maintaining the overall consistency of the model with
experiment and experience.

If the postulate is true, then the target spot where the knot is
supposed to be is not a reference signal. It is a perception. So is the
position of the knot; that's another perception. The answer to the
puzzle is now staring you in the face. To show you what it is, all Ihave to do
is change the instructions (or you can do it yourself): keep
the knot 4 inches to the right of the spot.

This makes it clear that you are not controlling the knot in isolation.
You are perceiving both the knot and the spot, and you are controlling a
RELATIONSHIP between them. The reference condition for this
relationship, one assumes, often unconsciously, is "knot over spot." But
that is just one possible state of the relationship; if you always pick
that relationship, you will not realize that other reference-
relationships are possible, and the role of the spot will seem
ambiguous. In fact, the reference condition can be any state of the
knot-to-spot spatial relationship.

When you pick a target position like "knot 4 inches right of the spot",
you can now realize that you do not perceive the reference relationship.
You perceive only the actual relationship. If the knot is 8 inches right
of the spot, that is what you perceive, and nothing else. You do not see
a knot that is 4 inches to the right of the spot; the only knot you see
is 8 inches to the right of the spot (alternatively, the spot is 8
inches left of the knot). You "know" somehow that the knot and spot are
too far apart (or too close together), but you have no picture of the
correct relationship in your perceptions. This sense of "knowing" that
what you see isn't "right" is as close as you will get to perceiving the
reference signal or the error signal with your eyes open. The only way
to get closer is to close your eyes and visualize the knot in the
relationship you mean by "four inches to the right of the spot." Now the
reference signal is routed into the perceptual channels, and you are
perceiving the reference condition. Not everyone can do this easily;
some people seem unable to do it at all with visual images.

As soon as you open your eyes, the imagined relationship is replaced by
the real one; the knot is now too far from the spot. You are no longer
imagining the reference condition, but perceiving the actual "wrong"
condition. As you act, the sense of wrongness diminishes and finally
vanishes -- but you are never perceiving anything but the actual

This is why we have a model. The reference signal and error signal in
the model are not part of experience. They are an explanation for how
action and experience come to be related as they are. We can't verify
their existence by looking at experience, because all that experience
contains is a perceptual report on the actual current state of affairs.
We can only test the conceptual structure of the control system
indirectly, by showing that it accounts for what we observe. Once in a
great while we can trace out some neural circuits, like those of the
spinal reflexes, and show that the physical architecture is consistent
with the model.

Relationships are the most difficult types of perceptions to understand
in the PCT model, because when we think of how the model works, we are
using our own relationship perceptions very heavily. The process of
comparison involves a relationship between the perceptual and reference
signals: perception smaller than, equal to, or greater than the
reference setting. But that relationship is detected automatically,
outside the purview of direct experience. It occurs at EVERY level, notjust the
relationship level; spinal motor neurons carry out this process
of comparison while controlling mere intensity signals. We have to
distinguish carefully between the behavior of the model, all parts of
which we view in the mind's eye using all our natural levels of
perception, and our experiences of the world and our actions on it,
which we view directly. Just remember that in this model all experience
is perception, and all perception is the output of a sense-organ or a
higher input function. Reference signals move in the opposite direction,
outward or downward, and save for imagination do not appear in the
perceived world.

It's ALL perception.



Bill P.