What is proficiency? Characterizing spoken language proficiency in older Spanish-English bilinguals

We conducted a detailed linguistic analysis of Oral Proficiency Interviews (OPIs) from older Spanish-English bilinguals (n = 28) to determine which cognitive, linguistic, and demographic factors predict proficiency. In the dominant language, older age was associated with lower proficiency scores, but aging effects were not significant after accounting for cognitive functioning scores. In the nondominant language, bilinguals with larger vocabulary scores, fewer speech errors, and higher education levels obtained higher proficiency scores. Multiple linguistic submeasures from the OPIs were highly correlated across languages (e.g., fast speakers spoke fast in both languages), but these same measures exhibited significant language dominance effects (e.g., bilinguals spoke faster in the dominant than in the nondominant language). These results suggest it is critical to control for cognitive functioning when examining aging effects on language production, reveal powerful individual differences that affect how people talk regardless of language, and validate the use of the OPI to measure bilingual proficiency.