[Martin Taylor 931110 18:00]
(Tom Bourbon 931110.1111) and, later (Rick Marken 931110.1230)
Martin and Hans, will either or both of you *please* tell me where I am
going wrong. When I read the words below, which I quote from posts by Hans,
I see Hans saying something very different from what Martin just said, yet
both of you agree that Martin sees what Hans intends.
Well, I can't speak for Hans any more than I have already (which is zero,
as any PCT'er will know). But I can try once more to explain the way
I read his writing, and what I think is going on.
Sometimes there is no feedback signal, either because it just isn't there,
or because you do not pay attention to it. Some more examples. (1) After I
switch off the light in my bedroom at night with the switch that is locat-
ed next to the bedroom door, I walk some 10 feet towards the bed, grab the
bedcover and get into the bed, all in total darkness. All the while, there
is no feedback whatsoever about my position relative to the bed. Yet I
grab and lift the bedcover accurately without fail.Martin and Hans, please explain to me where I am wrong when I see Hans as
saying, "All the while, there is no feedback whatsoever about my position
relative to the bed. Yet I grab and lift the bedcover accurately without
fail." If the words *I* mistakenly see really mean the person has lost input
to just one ECS in a hierarchy of ECSs and the remainder of the hierarchy
still operates with feedback control, *please* tell me how I too can make
that translation.
Isn't "my position relative to the bed" a perception in a relation-level
ECS? As I read it, that's the only one Hans was claiming to be deprived
of perceptual input. I see no reference to any changes in the rest of
the hierarchy (except, by implication, those that can be agreed to depend
exclusively on visual input). Whether Hans is correct about his claim on
that one ECS is a separate issue. Tom has pointed out that there are other
sensory systems that contribute to the perception of position relative to
the bed, so Hans may be wrong on the claim. But I read only a claim about
one ECS that Hans defined quite carefully.
Hans:
Please define kinesthetic control of walking in the dark in terms of
feedback processes only.Please, guys, does this reply by Hans really mean that the example of
walking in the dark is only about loss of input to just one ECS in a
hierarchy of many ECSs?
I can see a word "ONLY" at the end of the quote from Hans. He is asking
how you can describe the process as incorporating sensory input to ALL
the ECSs normally involved in walking in the dark. You can do this, by
showing that kinaesthetic, auditory and other senses can and do substitute
for vision in all ECSs involved.
Bill:
We don't just stride on ahead when the lights go out.
We go into a drastically different mode of behavior.Hans:
Your remarks are demonstrably false.
I guess I am wrong again -- and biased. Did I just see Hans say that when
Bill claims we use feedback when we walk in the dark, Bill's remarks are
demonstrably false? Or did Hans really say the person who walks in the dark
has merely lost feedback signals (shouldn't that be perceptual signals?) to
one ECS, not to all others in the hierarchy?
I didn't see any claim here about ECSs. I see a claim that one does
not immediately go into a different mode of walking, which is what I
read Bill as claiming. (Bill wrote a much better analysis of the situation
later (931110.0900)). I think Bill's statement IS demonstrably false,
if you include the expansions Bill also wrote, about feeling about for
landmarks and walking carefully and slowly. One does so after a pace
or three, depending on how familiar or well observed the place is, and
whether it had been seen to be free of obstruction. Initially, one can
perform quite well using imagined representations.
As a personal anecdote, one of my last actions before going to bed each
night is to put the cats into the kitchen and turn off the light. I
then walk three or four paces and put my hand on the door handle, usually
with no apparent error or hesitation. I do not have any apparent sensory
cues to the location of the handle relative to my hand between the time
I turn off the light and the time my hand closes on it. To quote Bill P's
brilliant (931110.0900) posting:
Walking in a
blacked-out room requires imagining one's position in the room, on
the basis of a model. The inputs to this model are now totally kinesthetic.
And do not, so far as I can see, provide by themselves adequate input
to the relation perception that is being brought near its reference. There
is no contemporaneous sensory input from the target, be it door handle
or bedclothes. The output from the relation-level ECS is, so far as I
can see, based on imagination. It is open-loop, providing references to
the lower control systems that DO control in the normal way. Those outputs
are based on a model of what the room is/was/should be, not on the difference
between a current perception of where I am in relation to where the target is.
Please, no more comments
about bias and misrepresentation and all-or-nothing thinking.
I definitely complained about all-or-none thinking, but I remember no
mention, either explicit or implicit, on the other two counts. If I
made any such suggestion, I apologize unreservedly. No such thoughts
were (consciously) in my mind. I know you too well for that. But I
do acknowledge suggesting that you might have misread Hans, inasmuch as
my own reading was different from yours, so one of us must have done.
Is that a comment about bias and/or misrepresentation?
ยทยทยท
====================
(Rick Marken 931110.1230)
I said:
...the first step in evaluating the value of a feedforward explanation
of a behavioral phenomenon would be to determine whether or not the
phenomenon involves control. If it DOES involve control then no
feedforward explanation is possible;Martin replies:
Substitute "is complete" for "is possible." Then I'll agree with you,
and so, I presume, would Hans.Feedforward does not provide ANY explanation of control. Please explain
what aspect of control is explained by feedforward (planned output).
None. See other parts of the posting to which this is a riposte.
For example:
3. I was under the impression that feedforward refers to a means of
determining behavioral results through computation of the outputs
that produce those results. This would mean that the result produced
by a feedforward process is NOT under control -- by definition.Right. Both the other constructs agree with this. I don't think
anyone has suggested otherwise, though I can see that you might have
implied it from some of the wordings used.
And much more, carefully describing the same, as, for example when I said:
In none of these cases
is feedforward related to "control" against disturbance. Only perceptual
control, which means a closed loop feedback system, can deal with disturbance.
We can't have much of a discussion on these terms, can we? I refuse to
defend positions that I explicitly deny, no matter how much fun such
an argument might be. It won't advance understanding. This is CSG-L,
not talk.bizarre.
How about re-reading that posting of mine, then Bill Powers' fine posting
of today (931110.0900 MST, quoted above), which lays out the situation
with much more clarity than I have obviously been able to achieve. I
could find nothing in Bill's posting with which to disagree (though I
might, if pushed, I suppose-- thinking of the phrase "Hans Blom to the
contrary" in context of how I read Hans). Bill's posting is not only
clear; it is wise. It should be among the archival postings that new
readers see.
Martin