Could you all be so kind as to remove me from the CC field on this discussion? You’re sending to the CSGNet so I get it there. I don’t need two copies of each and every one of these messages.
···
From: Bill Powers [mailto:powers_w@frontier.net]
Sent: Tuesday, December 13, 2011 6:14 AM
To: Control Systems Group Network (CSGnet); CSGNET@LISTSERV.ILLINOIS.EDU
Cc: warren.mansell@manchester.ac.uk; wmansell@gmail.com; sara.tai@manchester.ac.uk; jrk@cmp.uea.ac.uk; hy43@duke.edu; Sergio.VerduzcoFlores@colorado.edu; Brian.Mingus@colorado.edu; randy.oreilly@colorado.edu; Lewis.Harvey@Colorado.EDU; Tim.Carey@flinders.edu.au; steve.scott@queensu.ca; mcclel@grinnell.edu; marken@mindreadings.com; dag@livingcontrolsystems.com; fred@nickols.us; mmt@mmtaylor.net
Subject: Re: An idea about neuroscience
Hello, Andrew –
If you get your communications from CSGnet, be aware that your simple “Reply” doesn’t include any of the poeple in the CC list here if they aren’t on CSGnet.
Yes, I would think the scientific community would be more open to PCT. It may be partly a lack of assertiveness on my part, but on the other hand it might come from too much of it. Hard to develop the right attitude. All we can do is try to get better at communicating and keep control of our tempers. I think we’re gradually getting there, though.
Best,
Bill P.
At 12:52 PM 12/12/2011 -0500, andrew speaker wrote:
BP
PCT and the particular engineering background it came from are cuckoo’s eggs in the neuroscientific nest. If that’s not OK, now is the time to say so.
I thought it interesting that you used this analogy. As you probably know, many cuckoos lay their eggs in a host nest, often choosing the nest based on eggs that look similar. The cuckoo chicks are ‘encubated’ inside the cuckoo for a little over 24 hours longer than a normal bird before laying it’s eggs and so the cuckoo chicks hatch sooner and kick out the other eggs in the host nest before they are born. They have a ‘head start’ so to speak.
I guess this is how I think of PCT in my very limited understanding, it just has a head start on many other theories that I have seen. I found PCT via MOL and Carey’s work and so I have read many of the reasons you and your wife have written about why it hasn’t been more accepted in the psychological field and the resistance of people to toss aside the theories they have based their life work upon, but I still have a hard time understanding it’s lack of more wide spread acceptance. I would think the ‘scientific’ community would be more open to new ideas, especially ones that are validated with testing. While I know PCT is still ‘under construction’ and ‘evolving’, as any idea should be when its goal is finding the truth and not simply stubbornly maintaining its own dogmatic principles, it still surprises me it isn’t more wide spread. As Tracy and others pointed out, it is even able to incorporate and complement elements of evolutionary theory and others. I fully admit that I am not aware of all the competing theories out there, I can only try and assimilate so much new information at once. I really do appreciate all the hard work you and others have done. Reading thoughts from you, Roy, Carey, Ford, Marken and others has helped me better understand myself and is already assisting me in helping others, so thanks to you all…
Andrew Speaker
Lions For Change
3040 Peachtree Rd, Suite 312
Atlanta, Ga. 30305
404-913-3193
www.LionsForChange.com
“Go confidently in the direction of your dreams. Live the life you have imagined.” – Henry David Thoreau
On Dec 12, 2011, at 10:50 AM, Bill Powers wrote:
Hello, Henry et al–
At 05:56 PM 12/12/2011 +0800, Henry Yin wrote:
Hi Martin [Taylor],
I have no problems with Branco’s findings. It’s his interpretation
that I question. What his findings suggest is that you can build
“detectors” of AB but not BA with just the dendritic properties.
Let’s say AB is centripetal activation but BA is centrifugal. So AB
fires the cell and BA doesn’t. He’s just saying we don’t necessarily
need circuit mechanisms. But regardless of how you do it, you are
still left with the problem of explaining behavioral sequences, or
sequences of letters, and so on. Even if we accept his findings (and
so far it’s still too early to tell), that doesn’t mean you just use
dendrites to compute behavioral sequences.
A subtle and important point that I hadn’t considered. It’s perfectly true that a cell may “fire” when B occurs just before A but not the other way around – yet the firing may not constitute perception (conscious or unconscious) of the sequence. It all depends on whether the system receiving the firing signal experiences this as information about sequence. For example, if an inhibitory spike precedes an excitatory one closely enough, the excitatory one may not cause a firing because the inhibition hasn’t died away yet, but reversing the sequence could allow it. Even the refractory period after one impulse could prevent a following one from having an effect, while just a little longer delay would allow both impulses to be effective (in either order). These are phenomena of sequentiality, yet may not have any significance in the brain’s operation.
I am suspicious, in addition, of the concept of a cell “firing,” which is why I put it in quotes. That term makes it sound as if once the cell has fired, the message has been delivered. I don’t think a single impulse is informationally, behaviorally, or experientially significant. A sustained train of action potentials is required to make a muscle tighten and relax in the pattern needed to produce even the lifting of a finger. A subjective experience that lasts for less than a tenth of a second probably never happens. One spike comes and goes in a millisecond.
It’s all too easy to forget that according to all we know about perception, the world we experience is the world of neural impulses – stop the impulses and there is no experience. Whatever we say about the meaning of neural signals has to be consistent with the properties of the world of experience which we observe directly. For example:
It is said that neural signals are exceedingly noisy, yet I have yet to find anyone who reports that experience is noisy; mine is not, and I feel safe in asserting that nobody else’s is, either, except perhaps under conditions of extremely low stimulus intensity or when low-frequency noise is artificially introduced to test some theory. The signal-to-noise ratio of all my experiences is, under almost every condition, excellent. I may be uncertain about the meaning of an experience, but that uncertainty is detected with excellent smoothness. If I am uncertain, there is no doubt that I am uncertain.
This tells us something about the basic unit of neural information: it is not a single impulse or a low-frequency train of impulses, and perhaps it is not even a train of impulses in a single axon. That’s why I keep mentioning the redudancy of neural signals: we evidently experience the average of many redundant signals over some finite period of time like a few tenths of a second or more.
If smoothness of experience were not the case, I would have had to think twice about offering my tracking model or most of the others. My models are basically implemented as analog computations, even through carried out on a digital computer. A “sudden” change in the tracking model is a waveform that may take two tenths of a second or longer to change from 10% to 90% of the way from initial to final value (a standard measure of “rise time”). That’s long enough for 50 or 100 neural impulses to occur, and if we think of redundant channels as we must, probably more like 500 to 1000 impulses. That’s why I can get away with representing neural signals in the model as simple continuous noise-free variables. Adding noise to the tracking model makes its fit to real behavior worse. And the fastest changes are not “responses” – they are outputs of continuous transfer functions best described by differential equations, not digital logic.
PCT and the particular engineering background it came from are cuckoo’s eggs in the neuroscientific nest. If that’s not OK, now is the time to say so.
Best,
Bill
A neuron receives thousands of inputs-thousands of synapses on
different dendrites. The sequence of activation of these synapses
matters, as he shows, which doesn’t surprise me. But he asked whether
neurons can tell the difference between the words danger and garden.
And this is not a question you can answer simply by looking at
dendrites, in my opinion. The cell does not discriminate between
danger and garden and provide such information to the homunculus.
And even if a cell did, so what. A lot of cells have been shown to do
all sorts of things. To me that doesn’t explain much. I can tell
apples from oranges, and if you find a neuron in my brain that does
that (a lot of neurons can do that) you have not explained the
mechanism. You can’t say, Henry can tell the difference between
apples and oranges because there is a cell in his temporal cortex that
can tell the difference between apples and oranges and this cell tells
Henry that, look, this is an apple and that is an orange. This is
like Moliere’s dormitive faculty. It’s a disease in systems
neuroscience. There is a whole school that tries to find neurons that
discriminate stimuli as the monkey does. So you record a thousand
neurons and find 54 whose activity mirrored the monkey’s performance.
Then they think they are finished. I say, wait a second… Actually I
just feel sorry for the monkeys.
In the end, people are often trapped by words. Sequence is a word, so
it’s easy, all too easy, to go from this ‘sequence’ to that
‘sequence.’ Not exactly the same. Requires more thinking to unpack it.
H
On Dec 12, 2011, at 1:26 PM, Martin Taylor wrote:
Henry,
You know more about neuroscience than I ever will. Do you make this
judgment after reading the essayist’s published papers which he is
apparently summarizing very briefly in the essay?
Martin
On 2011/12/11 8:44 PM, Henry Yin wrote:
Hi Bill,
The essay is about some uncaging work done by the author. He is
definitely overinterpreting his data, in my opinion. Sequence in
his sense of the word is not the same as behavioral sequences,
which as you say requires a circuit mechanism, actually a very
large circuit (think whole brain) mechanism. People who do
dendritic work have to explain the relevance to a general audience,
but in this case there is no evidence of careful thinking. As
usual, I have no idea why Science publishes this stuff. Really
reminds me of dinner conversation I often have with other
neuroscientists.
Henry
On Dec 12, 2011, at 12:35 AM, Bill Powers wrote:
Hi, Martin –
At 11:17 PM 12/10/2011 -0500, Martin Taylor wrote:
I’ve been dipping in and out of this thread, and maybe this essay
from Science has been mentioned, but in case not, the attached
two pages seem fairly relevant to the recent discussion. If I can
quote one sentences from the summary:
Overall, the results of this research show that dendrites
implement the complex computational task of discriminating
temporal sequences and allow neurons to differentially process
inputs depending on their location, suggesting that the same
neuron can use multiple integration rules.
BP: Yes, I saw that and it’s one reason I want to include input
transfer functions if possible. Judging from the kinds of
variables human beings can perceive and control, it’s pretty
certain that neurons can do more than just weighted summation. The
problem is that I have no idea what sorts of computations are
required to create perceptions of all the kinds we’ve talked
about, so I might not recognize a useful function when I see it.
We really need some good applied mathematicians like Kennaway who
understand all the ins and outs of analytical geometry, physical
dynamics, maybe even tensor analysis (for computing invariants).
Or who can learn what they need to know. I don’t have a big enough
mathematics bump.
I don’t recall much about the article, but I remember thinking
that maybe the idea of “sequence” detection was a case of
overinterpreting the data. Couldn’t that neuron just be the output
of a whole neural network? I think that circuits, not just single
neurons, are needed to detect sequence. Perceiving the sequence
“A, B” as different from “B, A” requires the ability to remember
(or otherwise be affected by the fact) that A has already occurred
at the time B commences, doesn’t it? Maybe there is some process
that doesn’t need memory that can do this, but at the moment I
can’t think of what it might be. In the PCT model, sequence
detection occurs at a high level – the eighth of eleven. My
pseudo-model, in chapter 3 of B:CP, uses a whole string of pseudo- neurons hooked up like latches to accomplish the memory effect.
The last neuron in the string might appear to respond to a
sequence, but the other neurons are needed, too.
Best,
Bill