At the end of May I attended a terrific workshop organized by David Poeppel for the NSF. Here’s a link to the roster and the background papers we were given. The confab was fun, largely because the free wheeling discussion was based on some uncontroversial givens, first and foremost among these being that all accepted that something like Marr’s view was a reasonable idealization of the kinds of levels required to link brain and mind. In particular, all bought into the view that cognitive neuroscience needs good high level descriptions of the computational competences that the brain has in order to understand how it is organized at the neural level. Indeed, Randy Gallistel (to only a very few grumbles) proposed a much stronger version of the Marr thesis: that brain architectures cannot be fruitfully studied at all in the absence of good computational level accounts. It was further accepted that models of linguistic competence of the generative variety are paradigmatic instances of such Marrian computational level theories.
So, given this wonderful coming together of minds, what did I learn? Here are some recollected personal highlights.
First, We don’t actually know much about the neural bases of mental computation and so it is unreasonable to give neuronal level accounts a privileged status. One of our pre-conference readings (c.f. Mausfield here) has the following juicy quote:
Given that we presently know next to nothing about the physical principles underlying mental phenomena and achievements, there is no reason to assign the level of neurons a privileged explanatory role. (p.4)
This was not a point avidly disputed by the neuroscientists present, despite the acknowledgment all round that neuroscience has made impressive progress over the last 25 years. This is not incompatible with the realistic appraisal that there is a very long way to go and that, at this time, what we know about the brain offer few constraints on possible computational level theory (e.g. on linguistic proposals about the structure of FL/UG). We might wish that things were different (I know that I do) but they aren’t.
Evidence? Well, here’s one: it seems that for much simpler systems e.g. C. elegans with all of 302 neurons (whose wiring we know), why it does what it does is still a mystery. As Mausfield observed: “In the case of C.elegans, the complete knowledge of the components of its biological hardware would constitute a particularly favorable situation for understanding its complex behavior…” Nonetheless, Mausfield quotes a recent review that notes that despite knowing all we might wish to know about the 302 neurons in these nematode brains these reductive efforts have proven quite unsatisfactory: “C.elegans responds behaviorally to the presence or absence of food in a plethora of ways…Surprisingly little progress has been made in understanding these responses” (p.3 note 2)).
Second, this relative ignorance is nothing new. It seems that the goal of understanding mental phenomena in neurological terms has been a long-standing project, at least since the 18th century. In other words, this is not a bold new surprising thesis, despite what some hyperventilating philosophers might suggest. Again as Mausfield put it:
For over 200 years, the premise that mental processes must be considered a function of the brain has been more or less commonplace. This has deluded us into overlooking the fact that…our theoretical understanding is next to nil of what exactly…this function might actually be taken to be. (p.3)
It seems that Priestly (of chemical fame) already thought that this was the obvious scientific position to take (LaMettrie preceded him by a century or so). However, Priestly was considerably more modest than many of our current neuro-philosophers. His position was described as follows by the London Encyclopedia (1829):
Dr Priestly apprehends that sensation and thought necessarily result from the organization of the brain…but he professes to have no idea at all of the manner in which the power of perception results from organization and life.
A becoming modesty, I think!
Third, historically, computational level theories have generally laid the groundwork for neural explorations rather than brain functions constraining higher level accounts. Once again here’s Mausfield:
…advances in our psychological understanding of perceptual phenomena have in the first place benefited and fostered neurophysiology rather [than-sic] the other way around. (p.2)
The implications of this for Generative Grammar (GG) are pretty clear. GGs provide computational level accounts of the mental powers of native speakers; a descriptively adequate grammar of L describing the mental states of a competent speaker/hearer of L and an explanatory adequate theory of L describing how L derives from FL/UG given the PLD of L. These computational level accounts, one hopes, will serve to guide neuro-scientific research. How? Well, in much the way that Barlow (quoted in Mausfield) envisioned for work in the psychology and physiology of perception:
As to the claim that a theoretical understanding of visual perception derives from neurophysiological investigations, Barlow (1983, p.11) emphasized: “Nothing could be more misleading, for all the important properties of the visual system were first established by psychophysical and psychological observations made on the system working as a whole. […] physiologists need to be told what the visual system does before they can set about the difficult task of finding out how it does it. (p.2)
Substitute FL for ‘the visual system’ above and you have more or less the current state of play in the cognitive neuroscience of language, at least as seen by the cohort of people that David managed to get to sit down together to discuss these matters.
Fourth, to the problem that Poeppel and Embick (P&E) (here and here) identified as the “granularity mismatch problem” is still with us. In my presentation, I suggested that one of the virtues of the Minimalist Program (MP) is that it offers a way of bridging the divide that P&E identify. In particular, if we can really unify grammatical phenomena and reduce them to a common Merge-like core, then this will provide a convenient target for neurophysiological investigation: find a Merge-like circuit. Thus, the grammatical project described (e.g. here) was not dismissed as irrelevant to finding ways of incarnating minds in brains.
Fifth, I got a great peek into how neuro/psycho types are thinking of basic operations in their respective domains, c.f. Dave Heeger (here) and Greg Hickok (here) for a pretty good taste of what they are doing. Dave Heeger’s talk had, what to my ear, was a real minimalistic theme: how “ set of canonical neural computations” shared across different “brain regions and modalities” could apply “similar operations to different problems” (51). In the best of all possible worlds, we would love to find something similar in cognitive domains including language. Greg’s talk showed how we might integrate higher level psych-linguistic descriptions of speech, with lower level articulatory motor control. What to me was very exciting were the analogies between headedness in syntax and similar notions in motor plans, which appear to have similar kinds of structures. All of this was very speculative, and hence extremely interesting.
Sixth, Elisa Newport gave a fascinating presentation focusing on brain specialization for speech. She made (at least) two fascinating points. First, she observed that brains in which the language areas are compromised can redirect this function to other parts. However, not to just any other part. Rather, a brain can redirect linguistic capacity from a left language impaired hemisphere to the very same place in the other hemisphere. This suggests two things: (i) that either hemisphere can adequately subserve language and (ii) that the same regions in both hemispheres are particularly well suited (specialized?) for the kinds of operations language demands. In other words, though young brains rearrange the cognitive furniture, not all parts of the brain are equally adept at filling in for missing linguistic capacity, viz. brains are labile but not arbitrarily so. Second, Elisa asked a terrific question: why is the language area located where it is? And she shot down one plausible answer: it sits between the perceptual regions that care about audition and the motor regions that move lips and tongue. This, Elisa noted, cannot be the whole answer for the exact same regions subserve ASL speakers (a point also made by Helen Neville), and ASL speakers don’t much worry about audition or lip/tongue movement.
Last, Bob Berwick gave a great presentation on genetic differences between us and our Neanderthal cousins. The main finding is that we are almost identical! There were very very few differences. In effect, the minimalist assumption (that whatever happened that allowed language to emerge was both rapid and genetically “minor”) seems on the right track. I am in the process to trying to convince Bob to post on this, so stay tuned.
There was much much more; great presentations, excellent lunches, a terrific supper, lots of discussion, jokes, arguments, speculations and general good cheer. However, most heartening of all was the realization that there is a reasonable group of people out there that have no problem with the standard (Chomskyan) Generative view that linguistics is an important part of the cognitive neurosciences. I can only only hope that this view becomes even more widespread. If it does, it suggests the coming of a golden age.
 Bob Berwick made the reasonable point that restricting matters to three levels is likely a radical simplification, apparent if one considers how many levels computer engineers postulate to get one from programming languages to machine code. So, the Marr perspective is best stated that there are at least three levels worthy of serious consideration.
 Quoted in Mausfield p.3.
 I actually proposed that we should look for two circuits: one that combines elements and one that labels the resulting combination. The former is plausibly cognitively generic while the second is my candidate for the real distinctive linguistically special operation. However, the logic of MP does not require that my specific proposal be the right one (though, of course, I have no doubt that it is).
Norbert, thank you for the discussion and the link, it's very informative!ReplyDelete
In case David or Greg is reading this, it'll be great if similar stuff could be discussed as part of this year's Neurobiology of Language.
hyperventilating philosophers. :)ReplyDelete
Great discussion - thanks.ReplyDelete
"Substitute FL for ‘the visual system’ above and you have more or less the current state of play in the cognitive neuroscience of language,"
Marr just about inverts this in Ch. 1 (p. 28), pointing to linguistics as offering a model for building a computational theory absent an implementational account:
"Perhaps it is not surprising that the very specialized empirical disciplines of the neurosciences failed to appreciate fully the absence of computational theory; but it is surprising that this level of approach did not play a more forceful role in the early development of artificial intelligence [...] Chomsky's (1965) theory of transformational grammar is a true computational theory in the sense defined earlier."
He continues a few paragraphs later
"The explanation [for how transformations factor in to comprehension, roughly -- JB] is simply that finding algorithms by which Chomsky's theory may be implemented is a completely different endeavor from formulating the theory itself."
I take this latter point to offer a cautionary note to efforts to find a "merge circuit" or the like (Friederici and Grodzinsky push such a view in their 2006 review article), unless you adopt a Phillips-style parser/grammar isomorphism.