Theoretical Foundations of the Assessment of Bilingual Aphasia
Aphasia testing in only one language is not sufficient to assess language deficits in the polyglot.
-- Silverberg and Gordon ( 1979, p. 54)
The need to assess language capacities in both of a bilingual's (or all of a polyglot's) languages should be obvious for a number of reasons. Assessment is essential for purposes of diagnosis, research, and prescription for treatment.
The usefulness of the Bilingual Aphasia Test (BAT) for diagnostic purposes is twofold. When the language of the (hospital) environment is almost nonavailable to the patient, it is important to determine whether another language may serve as a means of communication. Only when both languages have been tested with a comparable instrument can one ascertain which language is better retained or less impaired. Conversely, subtle deficits may be observable in only one of the patient's languages. These deficits may nevertheless be suggestive of the general locus and extent of cerebral damage and would go unnoticed if the better preserved language happened to be that of the hospital environment and if the other language were not tested.
In both cases the results may help one to decide in which language the patient should receive speech therapy. In the first case, once it has been established that one language is definitely better preserved, decisions can be made with respect to the language community in which the patient may choose to live subsequently (e.g., back in the home country or in the country of immigration), and the language of therapy may be selected on the basis of the language of social reinsertion. In the second case, the language showing deficits would be treated.