Bilingual language switching has been studied extensively in cued picture naming paradigms, instructing bilinguals when to switch between languages. However, in daily life, bilinguals often switch freely, without external instruction. This study examined when and why bilinguals switch voluntarily. Spanish-Basque bilinguals frequently switched between their languages and their language choice was related to the ease of lexical access. Words that were slow to be accessed in Basque were more often named in Spanish and vice versa. In terms of response times, switching costs were observed not only in the cued but also in the voluntary task. However, while cued switching showed a mixing cost (reflecting the cost associated with using two languages rather than one), a mixing benefit was observed for the voluntary task. This suggests that voluntarily using two languages may be less costly than having to stay in one language.

This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement number 743691). Support was provided by a Ministerio de Ciencia e Innovación Grant #PSI2014- 53277, #PSI2015-65689-P, and by Ayuda Centro de Excelencia Severo Ochoa SEV-2015-0490.

Available online 18 Jul 2018