To determine the effect of bilingualism on vascular aphasia severity.

Bilingualism may affect the profile of cognitive disturbances associated with stroke. Its impact on aphasia severity, however, is in need of substantiation.

Our sample included 155 monolingual and 53 bilingual vascular aphasia patients. Bengali version of western aphasia battery (WAB), a validated scale, was used for language assessment. Bilingualism was defined as the ability to communicate in two or more languages during pre-morbid state of the participants in their interaction with other speakers of any or all of these languages. Participants underwent initial language examination during first week following stroke. Severity assessment was done by calculating aphasia quotient (AQ). Analysis was conducted by using the latest version of MATLAB software. Initially we computed the simple arithmetic mean of the two sets individually as well as conducted t-test using the AQ1 (initial severity) values. Subsequently, we distributed AQ1 in its four quartile segments and computed two major parameters of each quartile: (a) percentage of total patients falling in each of these quartile ranges for both bilingual and monolingual group, and (b) the mean of each of the quartile classes. In the next step, difference in aphasia severity between bilingual and monolingual groups was analyzed with respect to different variables: age, gender, type and location of stroke and lesion volume.

The overall difference in the mean aphasia quotient (AQ) between bilingual and monolingual participants was statistically significant (p=0.009) demonstrating a bilingual advantage. It was also found that in bilingual participants aphasia was less severe in certain subgroups, namely: higher lesion volume, male gender, and sub-cortical stroke, while in none of the subgroups a monolingual advantage was documented.

Current results suggest that bilingualism represents a protective factor in vascular aphasia; this effect is observed particularly in some aphasia subgroups.