Multilinguals' language control

For several decades, researchers have tried to explain how speakers of more than one language (multilinguals) manage to keep their languages separate and to switch from one language to the other depending on the context. This ability of multilingual speakers to use the intended language, while avoiding interference from the other language(s) has recently been termed "language control". At first, it was suggested that language control might be supported by a mental device for switching that allows speakers of two languages ("bilinguals") to go from one language to another (Penfield & Roberts, 1959), probably by turning one language on and the other off (Macnamara,Krauthammer & Bolgar, 1968). Subsequently, a multitude of studies showed that when bilinguals process one language, the other language is also activated and might compete for selection, discouraging the idea that languages could be completely deactivated. Parallel language activation was held for both reception (Dijkstra, Timmermans & Schriefers, 2000; Blumenfeld & Marain, 2013) and production (e.g., Colomé, 2001; Poulisse & Bongaert, 1994). According to the most influential model of language control developed over the last two decades, competition from the non-intended language is solved via inhibition. In particular, the Inhibitory Control (IC) model proposed by Green (1998) puts forward that the amount of inhibition applied to the non-relevant language depends on its dominance, in that the stronger the language the greater the strength of inhibition applied to it. Within this account, the cost required to reactivate a previously inhibited language depends on the amount of inhibition previously exerted on it, that is, reactivation costs are greater for a stronger compared to a weaker language. In a nutshell, according to the IC model, language control is determined by language dominance. However, inconsistent findings within the language control literature have questioned the validity of this account (e.g., Costa &Santesteban, 2004; Costa, Santesteban & Ivanova, 2006; Verhoef, Roelofs & Chwilla, 2009). The goal of the present dissertation is to investigate the extent to which language control in multilinguals is affected by language dominance and whether and how other factors might influence this process. Three main factors are considered in this work: (i) the time speakers have to prepare for a certain language or PREPARATION TIME, (ii) the type of languages involved in the interactional context or LANGUAGE TYPOLOGY, and (iii) the PROCESSING MODALITY, that is, whether the way languages are controlled differs between reception and production. To investigate language control in multilinguals, the four studies presented in this dissertation made use of the language switching paradigm with late unbalanced multilinguals (one stronger native language, the "L1", plus one or two additional weaker non-native languages, the "L2" and "L3", respectively). The effect of preparation time was explored by manipulating the interval between the language cue (indicating the language to use in the next trial) and the stimulus in a bilingual picture naming task as well as in a trilingual digit naming task. The role of language typology was assessed by comparing two groups of trilinguals performing a trilingual picture naming task. For one group, the L3 was typologically closer to the L2, but typologically more distant from the L1. For the other group, the L3 was typologically more distant from both the L1 and the L2. Finally, the influence of processing modality was explored by comparing a group of bilinguals performing a bilingual lexical decision (recognition) task and a bilingual picture naming (production) task. The results obtained in the four manuscripts, either published or in revision, indicate that language dominance alone does not suffice to explain language switching patterns. In particular, the present thesis shows that language control is profoundly affected by each of the three variables described above. Firstly, the data show that the cost of reactivating a previously suppressed language is dramatically altered by preparation time, rather than by language dominance. More precisely, results from the first two manuscripts reveal that, given ample preparation time, language switching costs for both the stronger and the weaker language can completely dissipate. This indicates not only that the cost of reactivating a language is not solely determined by its dominance, but also that language switching can be cost-free. Secondly, the present work shows that the way languages are controlled is affected by language typology. In particular, results from the third manuscript reveal that during language switching, typologically closer languages tend to interfere with one another to a greater extent than typologically more distant languages. Conflicts between languages are reduced by hampering the "disturbing" (stronger) language and/or by facilitating the "disturbed" (weaker) language. Thirdly, the present data reveal that language control is strongly modulated by processing modality. More precisely, the fourth and last manuscript shows that language control in reception seems to be modulated by language dominance, whilst language control in production appears to be regulated by a strategic controlling system aimed at optimizing performance. Overall, the findings obtained in the present dissertation indicate that language control in multilingual speakers is a much more dynamic system than previously believed and is not exclusively determined by language dominance, as predicted by the IC model (Green, 1998).