[From Bill Powers (2004.11.10.0701 MST)]
David Goldstein (2004.11.10.1755)--
[ Rick Marken (2004.11.09.0855)]
A reference state is a particular state of a perception which can vary.
So a reference state is a perception.
As a perception, it is built from lower level perceptions, I believe.
I can't tell who said this, but it needs to be corrected. A reference
signal is NOT a perception. For a comparison to take place, you need two
signals: the perceptual signal, which is the current value of a perception,
and a reference signal, which is a DIFFERENT signal set to the value that
In PCT as of 2004, all signals are one-dimensional, meaning that they can
vary only in magnitude (frequency). So a perceptual signal has a magnitude
that can vary, and a reference signal has a magnitude that can vary but is
set to one particular magnitude at a given time. The action of a control
system causes the perceptual signal to vary until its magnitude is the same
as the magnitude of the reference signal. A reference signal does not come
from a pattern-recognizing function; it is simply a signal set to have a
A perceptual signal is not patterned in PCT. It indicates by its magnitude
the degree to which a pattern is present in the set of inputs (lower-order
perceptual signals or stimuli), but it does not itself carry that pattern.
The pattern is recognized by computations in the neural network, the
perceptual input function, that generates the perceptual signal. The
pattern has no existence outside the neural network, or the computations
taking place in it.
I am simply describing here the basic principle of analog computing,
perhaps in a form that is strange. In an analog computer, what makes one
voltage mean one thing and another voltage mean something entirely
different is the nature of the physical process that receives one voltage
and generates the other. The physical process IS the "computation."
Integration of a voltage, for example, is done by
1. applying the voltage to a resistor to produce a current proportional to
2. Passing the current into a capacitor which charges up at a rate
proportional to the current, and
3. Detecting the charge on the capacitor as a voltage that is the output of
If the input voltage represents a force, the output voltage represents a
velocity. The input voltage, however, does not apply a force to anything,
nor does the output voltage have a velocity. They are both just voltages
with specific values at any given instant. If you did not know the
computation that derives the second voltage from the first one, you could
not tell what the second voltage means. If the first voltage could not be
identified as the coming from a force transducer, or a knob labeled
"force", you could not tell what it meant, either. Analog computation is
done without symbols, and the only rules of computation are those built
into the physical structure of the computing elements. Although patterns
can be recognized and acted upon, there are no patterns in any of the signals.
This is the whole basis of the PCT model. It is the basis of all the
computer demos developed in the last 30 years in PCT, and also in most
other fields that involve simulations.
Does it explain experience satisfactorily? No, I don't think so, not in the
sense of explaining why the world appears to us as it does. It explains
controlling very, very well. It predicts behavior very well. It even
explains well how it feels to control things. But you'll notice how the
"very"s drop off.It does not explain at all why red looks like red or why a
square looks square. Conscious experience is, so far, unaccounted for.
So a reference signal is not a perception. But then a perceptual signal is
not a perception, either. They are both just signals that can vary in
magnitude. What makes one a perceptual signal is that it comes out of a
perceptual input function. What makes the other a reference signal is that
it DOES NOT come out of a perceptual input function, and that it goes to a
comparator where it specifies a magnitude to be matched. The action of the
control system makes the reference signal into a reference signal, because
only the control system as a whole can make the perceptual signal's
magnitude match the magnitude specified by the reference signal, thus
demonstrating the primary effect of the reference signal.