Elliot Murphy

Recursion and Oscillations: Comments on Boeckx (2016) and Goucha et al. (2016)

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Cedric Boeckx has a new paper out in the Journal of Neurolinguistics, “A conjecture about the neural basis of recursion in light of descent with modification”. The central thesis is summarised as follows: “I argue that the expansion of the parietal region associated with the globularization of the neurocranium in our species contributed to the transformation of the connection between Broca’s and Wernicke’s region via Geschwind’s territory, and enabled the pairing of evolutionary ancient networks that together became capable of constructing and processing not just sequences, but sequences of sequences”.
Boeckx writes that recursion “rests firmly on primate cognition and neural circuitry”. More precisely, the paper claims that “the neuroanatomical reconfiguration of the parietal lobe brought about by globularization extended the Broca-Wernicke connection (to be precise, its dorsal dimension) into “Geschwind’s territory”, forming a fronto-parieto-temporal circuit that provides the basis for richer representational capacities, viz. recursive capacities”.
Here, he discusses and agrees with the Friederici-inspired story that the development of the fronto-temporal dorsal stream somehow brought about a shift from single-instance concatenation operations to hierarchically organised sequences. The additional detail Boeckx provides is to claim that the expansion of the parietal lobe – a consequence of a more globularised braincase – served to bring about the strengthening of dorsal stream connections. This in turn resulted in “the pairing of two evolutionary ancient networks (one fronto-parietal, the other fronto-temporal), both of which build and process sequences”. This idea has been expressed in Berwick and Chomsky’s recent book Why Only Us, and who were themselves re-articulating the findings of primatologists from the past couple of years. However, this story says nothing about how the brain actually implements what Boeckx refers to as “the nature of the computation (and algorithm) involved”.
Boeckx goes on to claim that this pairing of two streams (each capable of finite-state computations) “could have the effect of boosting computational possibilities. Instead of operating on one-dimensional sequences, one now operates on two-dimensional, ‘tree’ representations”. Boeckx believes that if the fronto-parietal dorsal stream were to be “combined (integrated) with another sequencing machine, sequences of sequences would naturally emerge as a result”. But this appears to be something of a magic step: Pairing two finite-state machines does not produce a higher-order device, and pairing a sequence with another sequence does not necessarily produce “sequences of sequences”. While it may be true that syntactic labeling plus a form of “spell-out” provides the human-specific features of language, and that both labeling and spell-out can be loosely (but only partly) attributed to the hierarchically organised fronto-parietal structures and the fronto-temporal loop connections to externalisation, the jump from single-instance concatenation to recursion likely required more than the pairing of two sequence processors.
Still, the paper is filled with attractive ideas, such as the following: “Perhaps the fact that the parietal lobe has long been associated with numerosity … may help us understand why syntactic structures exhibit a spontaneous ‘logicality’ … intimately related to quantification, processed by the fronto-parietal network”. There is almost certainly something to this, and as Boeckx is well aware the field could certainly do with more of these sorts of multidisciplinary gestures.
There are some very concrete proposals about the neurocomputational properties of brain waves with respect to language, for instance here, here, here and here. There does, however, seem to be much confusion concerning this oscillatory approach to language. Goucha, Zaccarella and Friederici (2016), for instance, make the following claim:
“Alternative mechanisms based on brain oscillations have been proposed as a crucial element for the emergence of language (Murphy, 2015b) … However, those mechanisms seem to already be in place in other species. For example, despite the crucial brain expansion that took place in primates and especially humans compared to other mammals, the rhythmical hierarchy of oscillations is mainly kept unchanged (Buzsáki et al., 2013). As Friederici and Singer (2015) pinpoint, the basic neural mechanisms behind cognition through the hierarchical embedding of oscillations are transversal across animals.”
However, while the hierarchy of brain rhythms themselves may be preserved, it is crucially their cross-frequency coupling relations which are human-specific – a major topic for future research.
References
Boeckx, C. 2016. A conjecture about the neural basis of recursion in light of descent with modification. Journal of Neurolinguistics http://dx.doi.org/10.1016/j.jneuroling.2016.08.003.
Goucha, T., Zaccarella, E., & Friederici, A.D. 2016. A revival of the homo loquens as a builder of labeled structures: neurocognitive considerations. Ms. Max Planck Institute for Human Cognitive and Brain Sciences, Germany.
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4 responses to “Recursion and Oscillations: Comments on Boeckx (2016) and Goucha et al. (2016)”

  1. cedric boeckx Avatar
    cedric boeckx

    Thanks Elliot for reading the paper and commenting on it. There are a few things I’d like to clarify, though, since you may have missed them.
    You are quite right that there is an aspect of Friederici’s model that I find interesting, and that no doubt a lot of other people find interesting (including Chomsky and Berwick, which I mention in the paper, by the way). But the point of the paper was to stress the possibility of identifying traces of descent in this ‘special’ dorsal circuitry, and avoid “only us” approaches to language. In a sense, the slogan is ‘specialized, yes; special, no”.
    You point out that “Pairing two finite-state machines does not produce a higher-order device” and seem to refer to a claim in my paper. But I address this point in the paper: I refer to works (such as Graf’s, or work I did with Uriagereka) stressing that we do not need to go beyond finite-state limits, so I am not claiming we necessarily need to produce a higher-order device (I think this is a very important point in the context of the paper, and the emphasis on decent).
    As for the observations about brain rhythms, you take issue, not with me, but with Goucha et al. I don’t address this point in the paper you blog about, but I should add that I side with Goucha et al. on this point: I think that cross-frequency couplings (theta-gamma, etc.) cannot be taken to be the source of human-specificity: they are the universal syntax of the mammalian brain, as Buzsaki would say. I suspect that connectivity plays a bigger role here: it’s not so much which frequencies get coupled with which ones, but rather which regions producing these frequencies can be interconnected. That’s why connectivity issues are central to the paper you comment on.

    Reply
    1. murphyblog Avatar
      murphyblog

      Thanks Cedric. On the whole, I did find your paper interesting and certainly framed within the right kind of neuroanatomical context. I’ll reply to your comments in turn:
      “(including Chomsky and Berwick, which I mention in the paper, by the way)”: My point was not that you didn’t cite the paper, since you do so even on the first page. Rather, I noted that the general “sequence pairing thesis” seems to be present in some form or another in Why Only Us (a book which I’m actually highly critical of).
      I’m in full agreement that the correct slogan should be “specialized, yes; special, no”. In fact that’s exactly why I’m interested in exploring cross-frequency couplings which are well-known to be highly conserved. As the papers of mine cited discuss, it’s certainly not just the phase-amplitude theta/beta-gamma nesting algorithms which are relevant to language (since as my recent Theoretical Linguistics commentary article notes, non-human primates are also capable of these forms of cross-frequency relations) but rather *where* in the brain these “extraction” and “maintenance” operations are taking place. So I’m agreement on your point about connectivity being central.
      When it comes to the finite-state issue, I did indeed notice your alignments with Graf et al in the paper, but my main issue was that the jump from “sequences” to “sequences of sequences” upon the ventral-dorsal pairing (again, as claimed in Why Only Us) would have to be given some kind of independent neurocomputational/oscillomic motive. So, going back to brain rhythms, this will likely be a nice way to blend the findings of the neuroimaging “cartographic” literature with the oscillomic work on attention, semantic memory, and phrase structure building. Of course there’s nothing special about hippocampal theta and thalamic alpha, but upon the emergence of a more globularised braincase (as you, and Antonio and myself have discussed recently) the generic extraction/maintenance operations of, for instance, the theta-gamma code would be able to “reach” into new areas previously cordoned off, so to speak (eliminating some of those “spatial inequalities” found in non-human primate brains).

      Reply
      1. cedric boeckx Avatar
        cedric boeckx

        Ok … so it seems you disagree with me far less than your original comment(‘s rhetoric) suggested. Good to know. I note in the 1st footnote of the paper that the proposal I make could relate to the one by Chomsky and Berwick, though I doubt it, because if it did, it would defeat their “why only us” point. The “sequence of sequence” step is argued for in my paper in part on the basis of the _hierarchical_ relation between Dehaene’s model and more modular networks (cf. my point about sequences of chunks). I still think you miss the point about ‘finite-state’, and it seems there is another point you miss: you mention “ventral-dorsal”, but I think one of the important points is “dorsal I and dorsal II” (Friederici’s insight, in my view). “Ventral” plays no role in what I discuss (i.e., I do not “jump from “sequences” to “sequences of sequences” upon the ventral-dorsal pairing”). Finally, if you agree with me about connectivity, not sure what the big deal about oscillation was in the original blog post. Anyway, thanks for reading the piece, and taking the time to comment, Elliot.

      2. murphyblog Avatar
        murphyblog

        My intention was not to point to a clear disagreement with your paper so much as it was to draw attention to current hurdles in investigating (and providing support for) its central claims. I get your reservations about the “only us” part of Why Only Us (something I share), but again that wasn’t what I was really interested in – it was more to do with the fact that the general loop-based architecture had been proposed in the book (and in some other places, too) and I found it odd that since you already cite the book in the paper you didn’t also note this similarity. I also get the point about the pairing of finite-state sequence processors, and in fact I got it straight away when I read the paper. As I said, I was puzzled by the sudden “jump” implied by pairing two sequence processors: How, in implementational/algorithmic terms, would the streams embed finite-state sequence X with finite-state sequence Y, yielding “sequences of sequences”? Finally, there’s no “big deal” about oscillations in the original post, it’s only a single paragraph and I was more interested in pointing to the (current) lack of a story here w/r/t linking the oscillomic code (developed in my own work) with the neuroanatomical novelties pointed to in Why Only Us, Friederici’s work, and much else (including the Theoretical Linguistics commentary article I mentioned).

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