Tuesday, August 1, 2017

Early thoughts on the Hickok & Poeppel dual stream model

I came across this email I sent to David Poeppel in July 1998 that sketches some of the basic ideas that congealed into our dual stream model.  You can see the starting point was David's prior work on word deafness and my thinking about how conduction aphasia fits in.  It's also clear that Nina Dronker's work on the insula was prominent at the time and in fact I had been corresponding with Nina about some of those details.  The comment at the end "Nina says grammar is in the anterior STS" was a reference to a presentation she gave on lesion correlates of sentence comprehension deficits that implicated the ATL.  David and I later convinced her to publish the study in our guest edited volume of Cognition in 2004.

Anyway, here's the text of the email:

ok, so the prediction that pure word deaf patients should have paraphasic speech seems to have panned out.  If the other prediction that PWD patients who had a left hemi infart first would have been classified as conduction aphasic before the right hemi lesion, then it might be interesting to further test the idea using rTMS.  Find a conduction aphasic with the left auditory cortex lesion, interrupt right hemi posterior auditory cortex function using rTMS and we should have an instant PWD patient with musical perception preserved!

Then all we have to do is figure out what the relation is between the posterior superior temporal plane, the anterior insula (a la Dronkers), Broca's area, and the SMG.  Damage to any of these areas seems to produce some sort of phonemic-like deficit, whereas damage to more lateral-posterior temporal lobe areas seems to produce more semantic type deficits (e.g., semantic paraphasics in Wernicke's and transcortical sensory aphasia).  Ok, I got it:  phonemic processing (undefined) is carried out in a network in the post. sup. temporal plane bilaterally, this network interfaces (1) with lexical-conceptual systems in the inferior temporal lobe (and elsewhere) via lateral posterior temporal lobe areas (wernicke's area, angular gyrus), (2) with phonetic-motor articulatory systems in Broca's area via the anterior insula, and (3) with conscious phoneme-based working memory systems in frontal and parietal lobes via the supramarginal gyrus (which is connected with frontal systems, I think).  Thus, the anatomical model of language is reduced to interface necessities (might I say, limited to those of virtual conceptual necessity) with:  (1) motor articulation systems, (2) conceptual-semantic systems, and (3) known working memory systems.  Find a place for grammar and we're home free!  Oh, Nina says grammar is in anterior STS, fine we'll go with that.

Sounds like a pheory to me.



William Matchin said...

"Thus, the anatomical model of language is reduced to interface necessities (might I say, limited to those of virtual conceptual necessity)"

And no Chomsky citations?!?

Greg Hickok said...

Yes, that was a direct reference to the then new tag-line of Chomsky's: "A virtual conceptual necessity." Hey, it was an email. No bibliography necessary. ;-)

Unknown said...

So, what made you drop the "phonetic-motor articulatory systems in Broca's area via the anterior insula" connection? And, any luck finding "a place for grammar"? :-)

Greg Hickok said...

It seemed likely that the insula was a lower level of coding than Broca's area. Then, later, the role of the insula at all in speech planning has been questioned. I still don't think we understand it well.

The ATL did emerge as a potentially important contribution: we did a lot of work on that over the years (look for co-authored papers of mine with former grad students, Colin Humphries, Kayoko Okada, and Corianne Rogalsky) concluding that the ATL is more about combinatorial semantics than grammar. Another former grad student, William Matchin, is pursuing the idea that the pSTS is a critical region for syntax, which has quite a lot of promise. I think proposals that the dorsal stream is playing an important role (e.g., see Friederici) is conflating syntax and working memory. Basal ganglia deserve more attention (e.g., see Michael Ullman's work for one line of argument).

Unknown said...

As you know, our data don't show the anterior insula is particularly important for speech production, regardless for stage of planning/execution. I'm still waiting for anyone to show that we are wrong...

Regarding grammar, it is probably futile to look for a specific cortical area that is "grammar specific," right? Looks like many different regions are important for different aspects for grammatical processing. We have been looking at this issue using lesion data and really haven't gotten anywhere in spite of having fairly large sample sizes. We still haven't given up on this issue. But, so far, there isn't much there... Regarding the basal ganglia and grammatical processing, Philip Lieberman made some pretty strong claims in this regard (if my memory from grad school serves me correctly...). Not a bad idea.

- Julius Fridriksson

William Matchin said...
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William Matchin said...

The idea that I've been pursuing is that the pSTS houses stored structural templates, which are a bit like elaborated lemmas from the production literature. The idea of lexicalized bits of structure is pretty well-accepted in the psycholinguistic and computational literature. This is a bit distinct from what is often talked about as a "grammar area", but would certainly be where stored structural information is stored. It's situated in the right place for connecting semantic processing (STS/MTG, angular gyrus) and sensory/perceptual processing (STG, MT, inferior temporal), which is how people traditionally conceive of as the role of syntax (e.g., the interface between sound and meaning). The VLSM aphasia literature I've looked at has found associations between sentence comprehension deficits (Pillay et al., 2017) as well as grammatical acceptability judgment deficits (Wilson & Saygin, 2004) and damage to this general area. I certainly don't think this is a "merge" area or anything like that. About the basal ganglia - I definitely think this is relevant, particularly with respect to language acquisition.

I'd love to hear more about what you are working on!