Bilinguals have been shown to perform worse than monolinguals in a variety of verbal tasks. This study investigated this bilingual verbal cost in a large‐scale picture‐naming study conducted in Spanish. We explored how individual characteristics of the participants and the linguistic properties of the words being spoken influence this performance cost. In particular, we focused on the contributions of lexical frequency and phonological similarity across translations. The naming performance of Spanish‐Catalan bilinguals speaking in their dominant and non‐dominant language was compared to that of Spanish monolinguals. Single trial naming latencies were analyzed by means of linear mixed models accounting for individual effects at the participant and item level. While decreasing lexical frequency was shown to increase naming latencies in all groups, this variable by itself did not account for the bilingual cost. In turn, our results showed that the bilingual cost disappeared when naming words with high phonological similarity across translations. In short, our results show that frequency of use can play a role in the emergence of the bilingual cost, but that phonological similarity across translations should be regarded as one of the most important variables that determine the bilingual cost in speech production. Low phonological similarity across translations yields worse performance in bilinguals and promotes the bilingual cost in naming performance. The implications of our results for the effect of phonological similarity across translations within the bilingual speech production system are discussed.

This research was supported by a grant from the European Research Council under the European Community's Seventh Framework Program (FP7/2007‐2013 Grant agreement no. 263575), three grants from the Spanish Government (PSI2008‐01191, PSI2011‐23033, Consolider Ingenio 2010 CSD2007‐00012), and the Catalan Government (Consolidado SGR 2009‐1521). This work, carried out within the Labex BLRI (ANR‐11‐LABX‐0036), has benefited from support from the French Government, managed by the French National Agency for Research (ANR), under the project title Investments of the Future A*MIDEX (ANR‐11‐IDEX‐0001‐02). We thank the Brain and Language Research Institute and the Féderation de Recherche 3C (both at Aix‐Marseille Université) for institutional support. Jasmin Sadat was supported by a pre‐doctoral fellowship from the Spanish Government (FPU‐2008). Clara Martin was supported by the Spanish Government (Grant Juan de la Cierva) and is now supported by the Basque Foundation for Science (IKERBASQUE) and the BCBL Institution. James Magnuson was supported by a U.S. National Institutes of Health grant to Haskins Laboratories (P01 HD001994, Jay Rueckl, PI).