The issue of language proficiency is often of central concern in working with a bilingual population and I’ve written about it before. Here, I want to continue that discussion and invite comments from both research and practical perspectives. So, the questions are:
What is proficiency?
How is it defined (or how should it be defined)?
How should it be measured?
All these questions are interrelated of course. So, what is proficiency? A quick google search of language proficiency yields 3,780,000 hits. Language proficiency +
grammar = 211,000 hits; vocabulary = 401,000 hits; use = 1,1550,000; exposure = 81,500; pronunciation = 63,500
I think that the differences in results among combinations has to do with different ways that proficiency is conceptualized. All of these factors go into proficiency. But, what’s the most important aspect of proficiency? From a very practical perspective I think it has to do with being able to communicate. From a research perspective however it likely depends on the question being posed. So, how proficient is person A on a measure of grammar or vocabulary (or both). What I think needs to be taken into account is that all these things are related but not perfectly. At the American Speech-Language-Hearing Association convention last year we presented data that shows similar but slightly different relationships among these in bilingual Spanish-English speaking preschoolers.
Even vocabulary comprehension vs. vocabulary production shows differences in which language and at which time children shift dominance. One nice example of this are a pair of studies (Kohnert, Bates & Hernandez, 1999; Kohnert & Bates, 2002) I think are highly informative with respect to proficiency. What happens is that Spanish-first-then-English sequential bilingual children show vocabulary gains in both languages over time. Older children score higher in both languages than younger children. Younger children show dominance in Spanish– as expected. Older children are dominance in English. What’s relevant to the issue of proficiency is that children’s cross-over to English dominance occurs at an earlier age in comprehension than compared to production. This means that at any one point in development you could demonstrate dominance in one language when measuring comprehension AND dominance in the other language when measuring production.
What about children who have language impairments? Or adults with aphasia? Or other groups of people with language-based difficulties. There I think that the task becomes even more difficult. Lack of proficiency can come from either lack of exposure or lack of language ability. What we’ve done is to look carefully at age of first exposure, amound of time each language is heard and used by the child. This approach isn’t perfect of course, but it’s a step in understanding the context in which the child is learning and using each language relative to how they perform on a given test (in each language).