NSD and PCT

CSGnet Archive CSG1995
1

[From John E. Anderson (950503.1745)]

Bill Powers (950502.0910 MDT)

Quoting me (950501.2245 EDT):

    NSD is important to me.

I presumed so. It is an unfortunate fact of human nature that we easily
fall in love with theories for their own sake, just because they have a
certain internal beauty. This is especially true when they are our very
own theories, our brain-children. The hardest task of a theorist is to
look the child over for birth defects, or to send the child out into the
mean streets of experimental testing.

However, I don't respect theories that are defended simply by saying
that one has spent a lot of time and effort on them. That doesn't make
them good theories, or right. It just makes them hard to give up when
dispassionate reason and evidence call for doing so.

NSD is important to me, yes. But when I said I had spent a number of
years developing it, I didn't mean that to be a defense of NSD, but merely
one reason why it is important to me. I am not committed to defending it
to the death. The "neuroactive envelope" idea, for example, is
"unconventional", to quote one prominent computational neurobiologist,
Terry Sejnowski of the Salk Institute, and I admit and accept that it may
well be wrong (technology is not available yet to test it). But I will
defend some aspects of NSD, such as the idea of synfire chains (not my
idea) and neurosemantic clustering (grouping of neurons with similar
function near one another), because I think that these are quite
reasonable and supported by experiment, and my interpretation of meaning,
because it makes sense to me. And I do not think they are incompatible
with PCT or useful only in S-R theory. Since you apparently do, then
would you (or Rick, or anyone else for that matter) please explain to
me what about NSD makes you think this, so that I can understand your
point of view? So far I have not seen any reason, dispassionate or
not, that convinces me otherwise.

Thanks again for your help. I anticipate asking for it again and again.

John

2

[From Rick Marken (950505.0900)]

John E. Anderson (950503.1745) --

I do not think they [concepts of NSD] are incompatible with PCT or useful
only in S- R theory. Since you apparently do, then would you (or Rick, or
anyone else for that matter) please explain to me what about NSD makes you
think this

I tried to explain this in a previous post but I'll try it again.

In a previous post you said:

NSD is a biological model of synaptic activity in the brain.

This would lead me to believe that NSD is an attempt to explain measured
properties of synaptic activity. I would expect to find no conflict between
NSD and PCT at this level. But then you started talking about how NSD
accounts for behavioral (not synaptic) phenomena. For example, you said:

I think the ability to predict such [perceptual] changes would be very
important for the organism's survival, because it would facilitate a quicker
reaction...I believe the predictive mechanism proposed in NSD could have
contributed to the evolution of functional localization in nervous systems,

So now NSD has a neurally implemented "predictive mechanism". This property
of the NSD model is not designed to account for synaptic activity; it is
designed to account for "quicker reactions" to perceptual changes. At this
point we have entered cause-effect land. In a loop "quicker reactions" to
perceptual changes are 1) ambiguous (are they lags or integration constants?)
2) not necessarily an improvment (reactions that are too quick can cause
instability) and 3) are not really "reactions" because they occur in a loop;
if you build a model of an apparent cause-effect relationship (like that
between perception and neural "reactions") that actually occurs in a loop,
your model is probably on the wrong track.

You said:

Let me emphasize that the responses I am talking about here are _neuronal_
responses, NOT the overall responses of the organism.

I just want to reassure you that I was well aware of that fact. But I was
also aware of the fact that all the "responses" of a living control system --
perceptual, neural, behavioral -- occur in a continuous causal loop; the
cause- effect relationships that exist between variables when this loop is
open change completely when the loop is closed.

NSD proposes that when a neuron is active, it releases a neuroactive
substance, which diffuses into the surrounding brain tissue to form an
"envelope" around the active neuron

How does this property of the model "explain" synaptic activity? It looks to
me like this is a neural model of more global behavior. It is from this
perspective that I saw NSD as a cause-effect model.

initial perceptual input representing the surroundings will be followed
within milliseconds by activity induced in adjacent neurons by new input
from the surroundings.

And again it looks to me like the model is not about explaining synaptic
activity; it is using assumptions about variables that influence synaptic
activity to explain how perceptual input leads to neural output . NSD is a
cause-effect model of an apparent cause- effect phenomenon. NSD seems to miss
the fact that the relationship between perceptual inputs and neural outputs
occurs in a loop.

Perhaps NSD really is just an attempt to model neural activity in the brain.
If so, I could see this better if you told me what data NSD is designed to
explain and what experiments would be done to test the model.

Best

Rick