Identifying the boundary between dialects and languages: The role of similarity and usage

The question of how to distinguish between dialects and languages has plagued linguists for decades. The present investigation uses behavioral observations to objectively distinguish between bilingual and bidialectal translation effects. Using the picture-word interference paradigm, Italian - Neapolitan (Exp 1) bidialectal participants named pictures while ignoring semantically identical, related, or unrelated distractor words presented in their two linguistic varieties. Consistent with prior investigations of dialectal lexical selection studies, we observed translation equivalent interference between dialectal varieties that were mutually non-intelligible and in participants who were active, proficient speakers of both varieties. Experiment 2 assessed the distractor effects in Italian-English bilingual speakers and did not observe similar translation equivalent inference effects. The results suggest that mutual intelligibility and high speaker proficiency are not necessary and sufficient conditions for establishing independent lexical systems.