Research on the cognitive consequences of bilingualism typically proceeds by labeling participants as “monolingual” or “bilingual” and comparing performance on some measures across these groups. It is well-known that this approach has led to inconsistent results. However, the approach assumes that there are clear criteria to designate individuals as monolingual or bilingual, and more fundamentally, to determine whether a communication system counts as a unique language. Both of these assumptions may not be correct. The problem is particularly acute when participants are asked to classify themselves or simply report how many languages they speak. Participants' responses to these questions are shaped by their personal perceptions of the criteria for making these judgments. This study investigated the perceptions underlying judgments of bilingualism by asking 528 participants to judge the extent to which a description of a fictional linguistic system constitutes a unique language and the extent to which a description of a fictional individual's linguistic competence qualifies that person as bilingual. The results show a range of responses for both concepts, indicating substantial ambiguity for these terms. Moreover, participants were asked to self-classify as monolingual or bilingual, and these decisions were not related to more objective information regarding the degree of bilingual experience obtained from a detailed questionnaire. These results are consistent with the notion that bilingualism is not categorical and that specific language experiences are important in determining the criteria for being bilingual. The results impact interpretations of research investigating group differences on the cognitive effects of bilingualism.

Research examining the cognitive consequences of bilingualism has increasingly relied on continuous measures to capture the degree and nature of bilingual experience, using such variables as proficiency, age of acquisition, and language environments. One such measure, language entropy, indexes the social diversity of contexts in which each language is used. The construct was developed in a particular bilingual context, Montréal, Canada. The present study investigated the extent to which it also applies to a context in which social language use is substantially different from that of Montréal – namely, Toronto, Canada. Following the procedures in the original study, participants were assigned an entropy score and performed the AX-Continuous Performance Task (AX-CPT). Performance was associated with self-rated language proficiency, but unlike the results from Montréal, was not associated with entropy scores. Therefore, differences in the language context influence whether language entropy is related to behavioral performance on a cognitive task.