So what is determined by language proficiency? And, we can ask this question looking at studies that have investigated the difference between semantic processing, that is a processing of meaning, and grammatical processing. You might recall from a previous section where I discuss two different studies. One using EEG that looked at a group of second language learners, this is work by Weber-Fox and Neville, in which these subjects varied in the age at which they learned English. And there was a second study done with FMRI done by Wartenberger and colleagues and in that study they also looked at groups of people that varied in when they learned the second language. And in the previous section we discussed results which showed that grammatical violations were in general more sensitive to when a person learned a second language. That is, if they learned a language early or late in life affected either the EEG signal or the brain activity observed during the processing of grammatical violations. In these two studies, the researchers also looked at what happens when there's a semantic violation. Semantic violation, as I noted in a previous section, something like I take my coffee with milk and dog, right? In that case what happens is that the word that's incorrect doesn't fit semantically. So in Weber-Fox and Neville's study, they looked at people who had learned English at various different ages. And what they found was that the age of when they learned English didn't matter as much for semantic processing. Now it's not that it didn't matter at all. They did find there were differences in the latest group, those who acquired English between 11 and 16. In that group they could see differences in the brain waves for semantic violations, for these errors in meaning. But in the earlier groups, they found roughly what looked like native types of N400 waves, these waves that occur at 400 milliseconds and indicate when a word is more difficult to process. And they appear in sentences like, I take my coffee with milk and dog. So only the latest group, those who learned English much later in life, showed a difference relative to the early learners and relative to monolinguals. Now, the interesting part about this is that these later learners were also lower in proficiency. They didn't speak English as well as the younger learners of English. This suggests that what modulates the ability to process meaning is the proficiency, the ability in that language. Wartenberger, using functional magnetic resonance imaging, found similar types of results. Those who spoke the language less proficiently show differences when processing these semantic types of errors. And this suggests there's a dissociation between grammatical processing being associated with early learning and semantic processing being more sensitive to how well somebody speaks a language.
