Bilingual Experience and Word Properties Selectively Affect L1 Picture Naming

Bilingualism is known to affect lexical retrieval speed, particularly in second language (L2) production, but its impact on native language (L1) naming remains unclear. We investigated how word-level properties (lexical frequency and cognate status) and individual experience with L2 (AoA, proficiency, use, and immersion history) shape L1 naming. English–French bilinguals were overall slower than English monolinguals, with the largest L1 naming costs being observed for low-frequency non-cognates, consistent with frequency-driven weakening of lexical representations. Exploratory individual-difference analyses revealed that current L2 use (but not L2 AoA, proficiency, or immersion history) predicted L1 slowing. Further, greater L2 use was associated with disproportionate slowing for high-frequency non-cognates. Together, the findings support two complementary mechanisms of bilingual lexical regulation: (a) long-term representational weakening that affects low-frequency, L1-unique words, and (b) short-term inhibition associated with active L2 use that slows highly accessible L1-unique words. These findings indicate that L1 naming costs are not global but emerge from the interplay of lexical characteristics and bilingual language experience.