Interpretation of Imaging Study Outcomes

1. Nonproficient Bilinguals

Although there has been no direct test of the role of proficiency as a determinant of variability in sites activated in the second language relative to the first, many of the studies propose proficiency (rather than age of onset of bilingualism) as a post hoc explanation of the discrepant results noted in the literature. However, only one study, by Perani et al. in 1998, actually compared two groups of late bilinguals varying in second language proficiency. In referring to their finding, Perani et al. echo the stage hypothesis:

A possible interpretation of what brain imaging is telling us is that, in the case of low proficiency individuals, multiple and variable brain regions are recruited to handle as far as possible the dimensions of L2 which are different from L1. As proficiency increases, the highly proficient bilin-guals use the same neural machinery to deal with L1 and L2.

2. Proficient Bilinguals

The predominant observation of overlapping activation in the two languages of bilinguals raises a question of its own. In the words of Perani et al.,

How do we reconcile the discrepancy we observe between the imaging data (largely similar activations with L1 and L2 in highly proficient individuals, regardless of age of acquisition) with ... behavioral findings [of L1-L1 differences even in early bilinguals]? ... We wish to raise the possibility that spatially overlapping networks to process L1 and L2 should not immediately be equated with competence, or performance identity.

So just how are we to interpret these results? The question resists easy answers, for as Perani et al. point out,

What our results show is thatfor the happy few late bilinguals that reach high proficiency, the (macroscopic) brain activation is similar to that ofnative learners of the language. What we do not know, however, is whether the similarity in brain activation is the consequence or cause of learning

L2 successfully. Further research is needed to clarify this point.

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