From: PSYCOLOQUY (Electronic Journal) <psyc_coglit.soton.ac.uk>
Date: Fri, 14 Aug 1998 12:01:26 +0100 (BST)
To: psyc_coglit.psy.soton.ac.uk
Subject: Psycoloquy disposition: Harpaz.
Cc: yeh_harlequin.co.uk
Dear Yehouda Harpaz,
Enclosed are the five referee reports on your manuscript: "The Neurons
in the Brain Cannot Implement Symbolic Systems".
Unfortunately, these reports do not give me a basis for accepting your
article for publication in Psycoloquy, nor for recommending revision
and resubmission. Although there are arguments and evidence in the
literature to the effect that the brain is not doing only symbol
processing, there is no reason to suppose that symbol processing cannot
be implemented by neurons.
Thank you for allowing Psycoloquy to consider your manuscript.
Sincerely,
Stevan Harnad
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Stevan Harnad harnad_cogsci.soton.ac.uk
Professor of Psychology harnad_princeton.edu
Director, phone: +44 1703 592582
Cognitive Sciences Centre fax: +44 1703 594597
Department of Psychology http://www.cogsci.soton.ac.uk/~harnad/
University of Southampton http://www.princeton.edu/~harnad/
Highfield, Southampton ftp://ftp.princeton.edu/pub/harnad/
SO17 1BJ UNITED KINGDOM ftp://cogsci.soton.ac.uk/pub/harnad/
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REFEREE #1 Anonymous
Ordinarily I would like very much to referee papers for you. In this case,
the claim seems so patently self-contradictory that it would be a waste
of time. What does the author think he is doing, if not symbolic
processing? And what does he do it with, if not neurons? What is
Broca's area for, if not symbolic processes ? Etc.
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REFEREE #2 Anonymous
I'd say it's nonsense -- just look at Minsky's book on Finite and
Infinite Machines!
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REFEREE #3 Anonymous
I reviewed this paper for another journal and rejected it as
having no substantial content.
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REFEREE #4 Anonymous
It's of no value. Moreover, I reviewed it in March for another publication; I
thought it was of no value then, too. Here is a copy of the review I sent
them. The author may have made some revisions since then; the section
numbers I reference below don't seem to match this version. But the
paper is not substantially different.
The author purports to show that brains cannot implement symbol
processing operations because they cannot copy tokens reliably. But he
admits in the first paragraph of section 7 that people can in fact
handle symbols. (And contrary to the claim made a few paragraphs
later, such symbols are not necessarily tied directly to sensory
inputs, since people are perfectly capable of manipulating sentences,
formulas, diagrams, and concepts they dream up in their heads.) So the
author tries to imply that just because people can handle symbols, this
does not mean that BRAINS can handle symbols. Actually, he doesn't say
something quite that ridiculous; he argues (p. 14) that "the components
of the brain" cannot handle symbols. But this is an entirely different
claim than the paper started out with and concludes with, i.e., that
the brain as a whole is not a symbol processor. Since no one ever
claimed that individual neurons or small groups of neurons were symbol
processing systems, the author's central argument is revealed as an
attack on a straw man.
The paper concludes with a long series of silly statements, such as
(p. 18) "handling language does not require any dynamic mechanism"
because the meanings of words are static. (What about the need to
dynamically construct representations of novel sentences?) And
(p. 21) "Neuroscientists do not realize the importance of the
stochasic connectivity for theories of cognition".
Obviously, this is not a scholarly paper. And the central argument is
nonsense. I recommend that the paper be rejected.
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REFEREE #5 Anonymous
This paper argues that the brain cannot represent symbolic systems. The
conclusion appears to be obviously false, the literature review is
shoddy, and the paper is not well-argued. Commentaries on this piece
are unlilkely to substnatially advance our understanding. I therefore
recommend against publication.
Symbols in conscious deliberate thought & Dualism
The reason that the argument appears to be doomed from the outset is
that the human brain appears to at least be able to simulate symbolic
systems in conscious, deliberate thought. Thus even those radical
connectionists who would deny that symbol-manipulation plays much role
in some areas of cognition make an exception for "serial, deliberate
reasoning" or "conscious rule application". For example, Touretzky &
Hinton (1988) wrote that
"many phenomena which appear to requires explicit rules can be handled
by using connection strengths [but...] we do not believe that this
removes the need for a more explicit representation of rules in tasks
that more closely resemble serial, deliberate reasoning. A person can
be told an explicit rule such as "i before e except after c" and can
then apply this rule to the relevant cases."
If the brain can manipulate symbols there, any argument with the
conclusion that the brain cannot manipulate (or represent) symbols must
be mistaken.
The author addresses this point briefly in paragraphs 47-50, but the
response given there seems incoherent. If the brain a whole can
represent symbols, then the brain can represent symbols. The author
seems to be resorting to a kind of dualism in which a person can
manipulate symbols, but a brain cannot. Everything we know about
cognitive neuroscience and cognitive neuorpsychology makes this sort of
dualism untenable.
Where has the author gone wrong?
As I reconstruct his argument the premises are as follows.
1. the processing in the brain is done by neurons.
2, every mechanism in the brain must be implemented by neurons.
3. neurons are stochastic.
4. stochastic neurons cannot implement symbols
Therefore
5. The brain cannot implement symbols.
Which premise is wrong? Premise 1 is likely right, but not entirely
beyond doubt; the same goes for Premise 2.
Premise 3 may be correct for some neurons and not for others. Here, the
author to some extent confuses gaps in our collective knowledge of
neuroscience with limitations on what is possible. One might have
formed a similar argument in Mendel's time to argue against the
possibility of their being genes.
The main problem is with Premise 4, a premise that rests more on a
poverty of imagination than on any in-principle argument. Note that
there is at least some stochasticity in a standard computer, albeit of
a different sort (e.g., radiation emitted from a sunspot might affect
the memory register that contains the thirty-seventh character in this
symbolically stored e-mail message). If we accept the fact that
sunspots introduce some stochasticity into computers, the form of
argument expressed in 4 would lead to the false conclusion that
computers are not symbolic. (The author seems to think that these two
kinds of stochasticity differ in an important way relevant to the
argument, but I am unable to follow the author's argument.)
Other general comments
The manuscript is unclear. Having read through this manuscript several
times, I still don't fully understand the author's argument. (Some
examples are listed below.)
The literature review is shoddy, which is especially worrisome since
the author frequently takes gaps in the literature to be indicative of
in principle arguments; often such gaps only reflect the authors's
unfamiliarity with the literature. (See various references below.)
Other comments.
Paragraph 7 is confusing. Isn't the storage of a symbol a kind of
computation?
Also, the requirement of arbitrariness seems unmotivated.
It's also not clear that symbols *must* be stored; one could build a
symbolic computer a la McCulloch & Pitts (1943) that passed along
symbolic activation values without storing them.
Paragraph 13: There may be mechanisms of short-term synaptic plasticity
that have not yet been identified. See Gallistel (1994) for an argument
that such mechansism must exist, even if they have not yet been
identified. Also, see Gallistel (1998, in the 4th volume of the
Osherson MIP Ress COgntive Science Introduction.)
Why can there be no way in which "distal events can affect the strength
of specific synapse"?
Paragraph 15: Maybe the selection of these neurons is systematatic, but
in ways that neuroscientists have not yet come to understand.
Paragraph 23. Point about cell populations is important, but should not
have been ignored in Section VI.
Paragraph 24 confuses "specialized" with "prespecified"; targets of
given vertrbrate neurons may not be prespecified but may still be
specialized. (See, e.g., Rakic, 1995).
Paragraph 24 Constructions like "worst example" (other examples may be
foudn throughout) are unduly condescending.
Paragraph 43. I don't undertsnad the argument and/or the evidence here.
Paragraph 52, 56. Re: behavioral tests and insights from symbols: The
work of Pinker on connectionism is very relevant here. (See (Marcus,
Brinkmann, Clahsen, Wiese, & Pinker, 1995; Pinker, 1991; Pinker &
Prince, 1988) Likewise, Fodor & Pylyshyn (1988) have argued that
symbols give the only account of compositionality.
Paragraph 53: No argument is given to show that the symbolic approach
does not work. Also, what would the author take as evidence for the
symbolic approach?
Paragraph 54: Even if symbols had not yet yielded insight in to
neurobiology, that would not mean that they couldn't. Again, Mendel's
postulate of genes took a number of years before it lead to direct
understand of molecular mechanisms.
References
Fodor, J. A., & Pylyshyn, Z. (1988). Connectionism and cognitive
architecture: A critical analysis. Cognition. 28, 3-71.
Gallistel, C.R. (1994). Foraging for brain stimulation: toward a
neurobiology of computation. Cognition, 50, 151-170.
Marcus, G. F., Brinkmann, U., Clahsen, H., Wiese, R., & Pinker, S.
(1995). German inflection: The exception that proves the rule.
Cognitive Psychology. 29, 186-256.
McCulloch, W. S., & Pitts, W. (1943). A logical calculus of the ideas
immanent in nervous activity. Bulletin of mathematical biophysics. 5,
115-133.
Pinker, S. (1991). Rules of Language. Science. 253, 530-55.
Pinker, S., & Prince, A. (1988). On language and connectionism:
Analysis of a Parallel Distributed Processing model of language
acquisition. Cognition. 28, 73-193.
Rakic, P. (1995). Corticigenesis in Human and Nonhuman Primates. In
M.S. Gazzaniga (Ed.), The Cognitive Neurosciences (pp. 127-145).
Cambridge, MA: MIT Press.
Touretzky, D.S., & Hinton, G.E. (1988). A distributed connectionist
production system. Cognitive Science, 12, 423-466.
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