Thursday, September 3, 2015

Brains with language

Humans speak and other animals don’t, or at least don’t like we do it. The qualitative difference is so obvious that only sophisticates could talk themselves into thinking that the linguistic capacities we find in humans are even roughly continuous with those found in other animal communication systems. If you are not a dualist, this suggests that there must be something different about human brains upon which this unique linguistic capacity supervenes.  Everyone would love to know what this difference consists in. In fact this desire makes even skeptical scientists (yes, this is ironic) trigger happy, for the moment anyone finds any difference between human brains and those of our “nearest” cousins this news makes a big splashy headline announcing the discovery of yet another breakthrough explaining how we got to be so verbose.  One example nice of this is a recent paper by Wang, Uhrig, Jarraya and Dehaene (WUJD) here.

Whatever the value of the results (I’ll discuss more details in a minute) the PR associated with it is quite breathless. Here is one example from The headline is “Breakthrough in understanding the origins of human language.” The result, if it bears on this question at all, apparently does so in an entirely modal way. What I mean by this, the most that one can conclude from this study (as the carfule wording quoted below shows) is that maybe the thing that WUJD finds relates to language in some way. But then again, many things might relate to language in some way. My own view, on a quick reading of WUJD, is that it is quite unclear which features of language (if any) the differences WUJD discovers between human and macaque brains explain. And if, per chance, we take recursion to be the most distinctive property of human language, then it is likely that the WUJD results tell us nothing at all about this most distinctive property. Let me elaborate.

The paper shows that humans treat sound sequences differently form macaques as follows. Both groups can track patterns (e.g. AAAB vs ABAB) and both can track different number of sounds (e.g. AAAB vs AAAAB). However, whereas in macaques this information is segregated in different parts of the brain, human brains have areas that are sensitive to both these parameters at once (i.e. there are areas in the human brain which integrate these two kinds of information). Moreover, it appears that the locus of this integration coincides with areas of the brain implicated in language processing (let’s hear it for Broca’s area!!)[1]. The big conclusion is “while some abstract properties of auditory sequences are available to non-human primates, a recently evolved circuit may endow humans with a unique ability for representing linguistic and non-linguistic sequences in a unified manner “  (my emphasis, NH, p. 1966).[2] Sure it may, but then again it may not. What neither the paper nor the reports discuss is what specific aspects of language this novel brain property is responsible for. In other words, granted that humans can do these things and that there are dedicated brain areas tasked with keeping track of this kind of joint information, which features of language does this newly enabled capacity underwrite. I have no idea.

And this is not good. As I’ve said many times before, we know a lot about the formal properties of human language. The paper is suggesting that being able to integrate two kinds of abstract information is useful in doing something linguistic. Ok, which linguistic thing is it useful for? I am pretty sure that it says nothing at all about the biggie Chomsky talks about (i.e. recursion) for the stimuli discussed involve simple unembedded templates. These are abstract, but not nearly as abstract as the recursive structures that natural languages generate. We can track these templates in the data for they create regular patterns there (see here). The problem with linguistic patterns is that there aren’t any in the absence of the generative procedures that give rise to them.[3] If by patterns you mean abstract templates, then much of language structure is without pattern. Which part? Well, at least the recursive part.

Of course, WUJD might be pointing to something else. Maybe the relevant patterns are not like out syntactic ones but more like phonological ones. Maybe. But then it would have been useful were WUJD to indicate how the kind of abstract information integration WUJD notes suffices for/is necessary for/ relates to the formal patterns we find in the sound structures or morphological structure or whatever structure found in natural languages. Absent this, there is little reason to think that the identified integrative capacity has anything much to do with language.

Let me say this another way. One contribution linguists have made to the cog-neuro of language has been to provide pretty well worked out formal descriptions of the kinds of rules we find in natural languages. These rules specify an endless variety of different kinds of possible patterns. Language competent brains must be able to compute these patterns using these kinds of rules. A brain based “breakthrough in understanding the origins of language” must discuss how brains compute these very well described structures. It is not enough to generically note that these structures are “abstract” or “algebraic” or “symbolic.”  Sure they are, but so are many other things as there are many (infinitely many?) ways of being “abstract,” “algebraic,” and “symbolic.” And given that we actually know something about the very specific ways that human languages are “abstract” and “algebraic” and “symbolic” it behooves those wishing to address the etiology of our linguistic capacities or their brain bases to relate their findings to these specific properties. It is simply not enough to note that our brains differ from “their” brains in some way (a typical example: area A is tied to B in us but not in them or our brains are round and theirs are oblong therefore…) and think that this tells us something about language. It really doesn’t. It certainly does not merit the kind of hype noted above. And this is from scientists, even ones that I admire.

[1] To be sure, it seems to be common wisdom that Broca’s area lights up in almost any fMRI experiment. In fact, I recall David Poeppel once snarking that one prerequisite of any well-designed brain experiment is that it light up Broca’s area.
[2] Is it only me or does it seem strange to anyone else that the comparison animal is the macaque? This I hardly a proximate relative in evo terms, is it? Nor, sor far as I know, is it much like birds, animals that are “phonologically” adept (see here). So why macaques?
[3] This very important point is made in Jackendoff’s mis-named intro text Patterns in the Mind.


  1. First line of the abstract from this paper: "The ability to extract deep structures from auditory sequences is a fundamental prerequisite of language acquisition".

    Two problems. (1) it's a false statement - have they never heard of sign language? (2) "the ability to extract deep structures" from the environment is a fundamental prerequisite for language acquisition, maybe, but so are a ton of other things - basic sensory processing of some kind, long term memory, motor control over some kind of effector, etc. What we're interested is not how people extract patterns but how people generate them. Chomsky once said that if they taught chimpanzees or gorillas to use sign language the way humans do that it wouldn’t matter – what is interesting is that humans spontaneously acquire language, without (and often in spite of) explicit instruction. This kind of empiricist dogma in cog neuro really bothers me – everyone focuses on getting something from the environment rather than the intrinsic dynamics of the system.

    Other quibbles with their experimental interpretation, of course. The best they can say is that humans have verbal working memory and monkeys don’t. BIG WHOOP.

    1. Though this is being very persnickety, it is worth noting that what they mean by deep structure and what linguists mean by it are entirely unrelated. They use this as a shorthand for some abstract structure. Linguists use it as the syntactic realization of thematic information. I actually found the (mis)use of this technical term in a paper about language quite annoying. But this is a small point.

  2. Now seems to be an appopriate time to leave a link to this XKCD comic on the blog. :p

  3. This Frontiers paper published today on the brain dynamics of linguistic computation might be of interest: