ms. #39-97:Harpaz. "The neurons in the brain cannot implement symbolic systems."

Dear Yehouda Harpaz,

Enclosed you will find two reviews of the ms. you submitted for publication in the European Journal of Cognitive psychology. Reviewer 1 is Dr. Pierre Perruchet. Reviewer 2 is Dr. Luis Jimenez.

While both reviewers express intertes in the issues you attempt to address, they also both indicate that your manuscript fails to address them satisfactorily. I will not repeat their arguments in details here as the reviews are quite detailed, but it should be obvious that there are serious problems at different levels, ranging from your writing style to the conceptual underpinning of your argument. The most important problems, based on my own reading of your manuscript, are (1) that your argument rests on poorly-supported speculations about the role and nature of stochasticity in the pattern of connectivity between neurons in the brain, and on erroneous assumptions about the implications of the physical symbol system hypothesis, and (2) that you fail to offer any convincing (alternative) account of how human human beings are capable of processing symbols that is not a rehash of well-known ideas, such as the ideas embodied in the connectionist approach.

Thus while the topic you address is extremely interesting (it is indeed at the core of many current debates in cognitive science), the problems described in this letter and in the accompanying reviews are severe enough that I can only reject this manuscript.

I am sorry that my decision couldn't be more positive. I hope that you willfind the feedback provided by the reviewers helpful as you continue to work on this topic, and that you will continue to consider the European Journal of Cognitive Psychology as an outlet for your research.


Axel Cleeremans

The European Journal of Cognitive Psychology.
Author: Yehouda Harpaz
Title: The neurons in the brain cannot implement symbolic systems.

The author claims that the neurons in the brain cannot implement symbolic systems, because the connections between neurons are not well defined at the individual level. Although this view may appear, at first glance, as challenging and stimulating, I believe that it does not hold after further scrutiny, for several reasons.

First, the author does not question the claim that the brain can implement symbolic systems, as he contends, but, far more restrictively, he challenges a strict computer metaphor of the central nervous system. What is not possible, according to the author, is that a symbol token, implemented as a pattern of neuronal activation, may transfer from a neuronal structure to another one. Apart from some distortion (I discuss all neuronal features, not only patterns of neuronal activation), this is reasonably accurate. However, this is the last reference to symbol tokens, and in the next sentence the reviewer returns to his bogus line of attack. The underlying model is the computer structure, in which the information may transfer from a system (for instance, ROM or RAM) to another (for instance, CPU) without any losses. Repeating the blunt lie from two sentences earlier. The problem is that I doubt that we can find anyone willing to advocate that actual brains are built as computers. Among many other reasons, there are far more direct neurobiological counter-arguments than the one put forth by the author, such as for instance those stemming from studies on brain injury (the author himself mentions in P.18 that the assumption that the brain has a computation centre "is in conflict with evidence from brain damage"). Obviously, we can think of symbolic systems without relying on a computer metaphor of the central nervous system.

My second concern is about the so-called stochastic nature of the connections of individual neurons. The author infers this from the observation of differences between brains. I wonder why we should expect to have the very same network between individuals, and between the two hemispheres in the same brain. The claim that (p. 8): "Since the low-level connectivity is different between individuals, it cannot be specified during development (by the genes or otherwise), and hence must be stochastic" is groundless. We know that individuals differ by both genes and environment on the one hand, and that neural structure growth depends on both kind of factors on the other hand. It should be a deep mystery if all nervous systems turned out to be strictly identical at the end. This does not mean that they are stochastic.

The third main problem is about section 7, entitled:"If neurons cannot perform symbolic operations, how can the whole person perform symbolic operations?". It is indeed a good question, but I find no good responses in the paper. The second argument, "the brain implements a learning and thinking system", is specially puzzling. It is told here that we "are not limited to the capabilities that are inherited in the genetic make-up of the person". Therefore, according to the author, the brain implements a learning system. However, "components in the brain do not have these learning capabilities, so they are limited in a way that the whole person isn't." I am not very familiar with the various textbooks on which the author relies, but if these textbooks do not mention that a neural network has learning capabilities, they are in need of serious revisions.

Given these major drawbacks, I pass over in silence a lot of other problems (such as the allusion in p.20 to author's own model -a model that "can explain thinking"- without any details nor references).

Overall, I believe that this paper is unsuitable for EJCP.

Pierre Perruchet.

Manuscript: The neurons in the brain cannot implement symbolic systems.
Author: Harpaz.
Reference: ECP 39.97
Referee: Luis Jimenez
General Recommendation: Resubmit/not suitable for EJCP

The central thesis of this paper is that, given the stochastic nature of connections of individual neurons, it is not possible for the brain to implement symbolic systems. The paper begins with a very brief description of the essential features of symbol systems, then includes a description of the main features of neurons in the brain, with special emphasis on their pattern of connectivity, and finally proceed to the discussion of its main thesis, namely that the symbol systems cannot be implemented through such kind of hardware. The rest of the paper is mostly a restatement of this thesis against several counter-arguments.


Although I am sympathetic with some of the arguments defended along the paper, i'M afraid that my general appraisal can not be positive, and that I can not recommend publication of the manuscript as it stands now. Maybe a substantial revision of the paper could be considered as a resubmission, but it would require a change in the focus of the article, and specially more convincing discussion of the its central thesis. This general appraisal is based on three converging reasons that are discussed below.

First, my reading of the paper has been hindered by what I construe as a problem of focus and style. The author adopts a polemicist style that struck me as inappropriate, mainly because he does not contend with other papers addressing the same topic at a similar depth, but only with the content of some textbooks that, of course, can not avoid to be limited in scope and relatively simplified. Although this kind of provocative style can sometimes be considered as healthy, I would have liked to find (more?) references to the current discussion between defenders of the classical framework and proposers of non-symbolic alternatives. On the other hand, the problem of focus arises at the very description of what a symbolic system is. Here, I simply fail to follow the author in his description of the description of the symbolic framework: I don't know why the two requirements that he points out in p. 5 are the "essential" features of symbolic systems and why the whole discussion of the paper should be based precisely on these two features. The author may be right, but my understanding of his points would have been largely benefited from a thorough review of the literature from which the author has inferred such conclusions.

Second, and besides the problems of style and focus, the main shortcoming that I find in the paper is that it does not present convincing evidence to persuade the reader about its main thesis: that neurons in the brain cannot implement symbolic systems. OK, he convinces me that it is difficult to do so, but I was already persuaded about that before reading the text. In my view, then, what the paper fails to do is to demonstrate that it is not possible, EVEN IN PRINCIPLE, for a brain made up of neurons to implement a symbolic system. The discussion in section 5 is an attempt to do so, but I think that it is not a successful one. My final impression is that, although the original pattern of connectivity among single neurons is stochastic, some learned patterns of connectivity over groups of neurons could present enough systematicity to be considered as symbolic. Paragraph #4 in p.12 actually suggests this possibility, but it is discarded too soon, in my opinion, based on the absence of a learning supervisor. I don't think that such a supervisor would always be necessary for learning, and I could imagine, at least in principle, a system that develops a symbolic structure out of non-symbolic, stochastic connectivity. Anyway, my purpose is not so much to demonstrate that the thesis of this paper is wrong, as to show that it has not been satisfactory demonstrated.

Finally, there is also a third reason that I envision as a real threat for the conceptual nucleus of the paper. As the author has accurately pointed out by way of counter-argument, the fact that people can handle symbols is enough to demonstrate that the thesis of the paper MUST be wrong. So to be entirely consistent, the author should state one of the following three claims: (1) people cannot handle symbols, despite the fact that they appear to do so; (2) the brain does not manage symbols, but there is some other structure, outside the brain, which does that;(3)some part of the brain does manage symbols, but it is not the part that is made up of neurons. All these alternatives seems equally unlikely, so that I would prefer to stick at the position that it is the brain made up of neurons which can, somehow, implement a symbolic system, although we currently are unable to know how. I don't want to be harsh, but I think that the alternatives proposed by the author are simply pointless, and that they do not worth serious consideration.


The paper does not reach the requirements to be considered for publication in EJCP. The issue is relevant enough to deserve discussion in a journal like this, but the paper fails to present a complete description of the relevant framework in which such a discussion should take place, and the arguments presented do not succeed in sustaining the thesis of its author. resubmission could be considered if the author is prepared to face those two challenges.

Signed: Luis Jimenez

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