MEASURING DEGREE OF BILINGUALISM AND ITS EFFECT ON COGNITIVE PERFORMANCE
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Bilingualism is a unique experience that has been shown to have a distinct impact on cognitive performance: disadvantages in language production (Gollan, Montoya, Fennema-Notestine, & Morris, 2005) and advantages in executive functioning skills (Bialystok, Craik, Klein, Viswanathan, 2004; Costa, Hernandez, Sebastian-Galles, 2008). However, some researchers assert that bilingual differences do not exist at all (Kousaie & Phillips, 2012a, 2012b; Paap & Greenberg, 2013). These discrepancies can have a substantial effect on neuropsychological assessment results, diagnoses, and treatment recommendations. The purpose of this study was to measure bilingualism in patients presenting for neuropsychological testing to determine the effect of degree of bilingualism on cognitive performance. Bilingualism was measured in an objective, continuous manner using the Peabody Picture Vocabulary Test (PPVT; Dunn & Dunn, 2007) to assess proficiency in English and the Test de Vocabulario en Imagenes Peabody (TVIP; Dunn, Lugo, Padilla, Dunn, 1986) to assess proficiency in Spanish. This bilingualism index was used to measure the effect of degree of bilingualism on neuropsychological test performance in English/Spanish bilinguals assessed in their dominant language. Archival data from 99 participants presenting for neuropsychological testing were used to examine the bilingualism effect on the following cognitive domains: shifting of set, divided attention, naming, lexical retrieval, and verbal working memory. With the exception of the BNT, results of linear regression analyses revealed no significant effect of bilingualism on cognitive performance in any of the domains measured. Future research may investigate alternative ways to measure bilingualism to facilitate proper diagnosis and treatment recommendations in a clinical population.