Monday, July 7, 2008
Summer Institute for Cognitive Neuroscience: Trade-off between neuroscience and linguistics
I just returned from giving a talk in the language session at the Summer Institute for Cog Neuro, which was held in Lake Tahoe. Beautiful venue, great weather (until the wind shifted and smoke from a fire in the area blew into the valley), and an interesting session.
The program was chaired by Alfonso Caramazza and included talks by Peter Hagoort, Kevin Shapiro (Caramazza co-author), Franck Ramus, David Caplan, Laurent Cohen, and me. I'm not going to go into detail about any of the talks - you can read all about them when Gazzaniga's The Cognitive Neurosciences Volume IV hits the bookshelves. Instead, I want to comment the one thing that made a serious impression on me as I listened to the talks and fielded questions on my own talk, namely, that there remains a serious gap between psycholinguistics and biology.
I have to confess up front that I didn't hear all of the talks: I had to miss Caplan's and Cohen's talk, which were given on the day after mine. Based on the talks I did hear, the contrast was striking between those of us who approach the cognitive neuroscience of language, with an emphasis on neuroscience versus an emphasis on (psycho)linguistics. For example, Hagoort talked about semantic unification, spending a good deal of time dissecting the ERP patterns associated with a range of linguistic constructions; he had little to say about the functional anatomy underlying these unification processes other than reference to some brain regions that might be generating these effects. Shapiro and Caramazza's talk was mostly concerned with the patterns of association and dissociation in morphological processes that one finds in brain damage patterns; again not much in the way of detailed functional anatomic networks. Franck Ramus talked about the genetics of language, providing details on the foci of genetic abnormalities associated with various language-related conditions, but provided little psycholinguistic detail using terms like "morphosyntactic deficits" to describe the language phenomena. Likewise, my own talk highlighted the role of specific brain structures such as the posterior half of the STS (bilaterally), posterior planum temporale (Spt) in various language processes, but I had little to say about the exact psycholinguistic processes involved and, like Franck, resorted to terms like "some aspect of phonological processing" and "sensory-motor integration."
Neither approach is right or wrong, or more or less important. They just reflect a different emphasis.
In some sense, listening to a talk from someone with a different emphasis can be unsatisfying. For example, Peter Hagoort asked me how Levelt's notion of syllabification fits into our Dual Stream model. My response: I don't know. Caramazza and Caplan both pressed me on what kind of representations live in the STS. My response: Maybe a phonological lexicon of some sort. Good questions that I hope to be able to answer some day, but to date, not very satisfying responses. Although I didn't, I just as easily could have asked Peter, or example, how the notion of semantic unification fits with the connectivity pattern between the anterior temporal lobe and BA45 (or whatever).
In the end, it is often hard to find points of connection between these different approaches to brain and language research, and I think the tendency is either to ignore findings/hypotheses from the research program at the other end of the spectrum, or to reject it. I certainly feel this tendency in myself (semantic unification or dissociations in morphological abilities don't help me understand the response properties of Spt, so why pay attention), and I can see how people from a psycholing model approach might tend to ignore or reject what we're doing (it doesn't clarify the nature of syllabification or morphological affixation, so why pay attention).
But this is the wrong mindset, of course. We are all interested in understanding the relation between neural systems and language models. We need to pay attention to what's going on at both ends of the spectrum and actively seek connections. We also have to understand that neuroanatomical models are not intended (at this stage) to be psycholinguistic models, and are necessarily (at this stage) more coarse in terms of processing stages/representations. Despite the fact that both the Dual Stream model and Levelt's model of speech production have boxes and arrows, they are not aiming to characterize the same set of facts. Hopefully the two types of models will converge and constrain each other in the end, but there need not be a one-to-one relation between boxes and Brodmann areas. At this stage in our field, it helps to approach a given paper, talk, or grant proposal with an "emphasis adjusted" mindset.