"Integration" is a major operation in language processing (and other domains). We have to integrate bits of sounds to extract words, integrate morphemic bits to derive word meanings, integrate lexical-semantic information with syntactic information, sensory with motor information, audio with visual information, and all of this with the contextual background.
Some theorists talk specifically about regions of the brain that perform such integrations. I've got my favorite sensory-motor integration site, Hagoort has a theory about phonological, semantic, and syntactic integration in (different portions of) Broca's area, more broadly, Damasio has been talking about "convergence zones" (aka, integration sites) for years.
Two thoughts come to mind. One, is there any part of the brain that isn't doing integration, i.e., how useful is the concept? And two, if the concept does have some value, how do we identify integration areas?
I don't know the answer to first question and I have some concerns about the way some in the field approach the second. W.r.t. the latter, a typical approach is to look for regions that increase in activity as a function of "integration load". The idea is that by making integration harder, we will drive integration areas more strongly and this will cause them to pop out in our brain scans. This seems logical enough. But is it true?
Suppose Broca's area -- the region that always seems to get involved when the going gets tough -- activates more in an audiovisual speech condition in which the audio and visual signals mismatch compared to when they match (an actual result). Let's consider the possible interpretations.
1. Broca's area does AV integration. It is less active when integration is easy, i.e., when A and V match than when integration is hard, i.e., when they mismatch because it has to work harder to integrate mismatched signals.
2. Broca's area doesn't do AV integration. It is less active when integration is actually happening, i.e., when A and V match, reflecting its non-involvment, than when integration isn't working, i.e., when there is an AV mismatch. Of course, this explanation requires an alternative explanation for why Broca's activates more for mismatch situations. There are plenty of possibilities: ambiguity resolution, response selection, error detection or just a WTF response (given the response properties of Broca's area I sometimes wonder if we should re-label it as area WTF).
Both possibilities seem perfectly consistent with the facts. Similar possibilities exist for other forms of integration making me question whether the "load" logic is really telling us what we think it is telling us.
There is another approach to identifying integration zones, namely to look for areas that respond to both types of information independently but respond better when they appear together. In our example, AV integration zones would be those areas that respond to auditory speech or visual speech, but respond best to AV speech. I tend to like this approach a bit better.
What are your thoughts?