[From Bill Powers (970918.0806 MDT)]
Mervyn van Kuyen (970918 CET)--
A network that is allowed to change the transformation of its sensory
input before this input is compared to a reference, will escape effective
reinforcement by making perception and reference alike (probably *without*
exerting any useful control). Therefore, I prefer calling this input
'reality' and not perception. Perception is the result of transformations
that are constantly adjusted, I believe, like the reference.
Yes, what you describe does happen: we sometimes change the goal when we
can't make a perception match it. With regard to the rest of your post,
however, you're talking about processes that happen on two very different
time scales. The adaptation of a neural net to create a transformation
between a set of inputs and a perceptual signal representing some aspect of
them happens on a very slow time scale; once you have learned to recognize
"distance," for example, your way of perceiving distance is not likely to
change much for the rest of your life. However, given this transformation,
you will perceive many different distances which can change over a time
measured in fractions of a second. You can act on the world to make a
perceived distance match a reference distance; that is what PCT is about.
Control of perception means controlling the _amount_ of a _specific kind_
of perception; the amount can be affected in real time; the kind can't.
I don't see why a network shouldn't be allowed to build its
reference from the bottom up. A servoing system has the innate tendency
to hunt, focus (not in the negative system dynamical sense), so why not
suggest that's what we all start with in our life? I believe
in the tabula rasa mind. Micro-architecture of the brain is not
genetically encoded (cf. Edelman).
I agree, and that is part of the more general PCT model that includes the
process of reorganization. I agree that we do not start life with the
micro-architecture of the brain in place. However, what I call "levels of
perception" do exist in that the specific kinds of computations required to
form each level are inherited as types of neurons and abilities to change
connections in different layers of the brain. Thus if we didn't have a
certain pre-existing architecture, we would never learn to recognize (for
example) relationships. Many simpler animals can't.
The PCT architecture consists of a large number (thousands, at least) of
elementary control systems at many levels, each of which (once it becomes
organized) controls a single one-dimensional perceptual signal by sending
outputs to serve as reference signals for multiple lower-level systems. No
system sets its own reference signal; the reference signal must come from
outside it. No system reorganizes itself; it doesn't have any properties
(in the basic model) that are concerned with changing its organization.
Reorganization is something that is done TO a control system by some other
process functionally (if not physically) outside it. A control system does
not form itself; it comes into being as a result of some other process that
acts by forming, and later changing, control systems.
A reference signal, in PCT, is a signal to which a perceptual signal is
compared. By definition, a reference signal is an independent variable
relative to the control system it enters. Its source lies elsewhere. And it
is specifically a _signal_ having the same physical form as a perceptual
signal. So a low-level control system (such as a spinal reflex) can't set
its own reference signal. That's not the organization of the PCT model.
If you're going to propose a different model, fine. But as long as you're
talking about PCT, there is a large number of interacting properties of the
model that have to be taken into account. If you start offering
alternatives to one part of the model, everything in the model will be
affected, and you should know what the effects of your changes will be.
Unless you simply want to start from scratch, you have to become familiar
with the properties of the model as it exists before you start fiddling
with it -- nothing is present in the existing model without a reason,
including the idea that reference signals for one level of control come
from systems of a higher level.
Best,
Bill P.
Thanks for your extensive and precise reply, I