Most bilingual lexical models assume that L1 and L2 either share the same semantic system, or are distinguished at the semantic level but connected through lexical associations. For example, the Revised Hierarchical Model (Kroll & Stewart, 1994) assumes the stronger access from L2 to concepts via the L1 lexical representation at the early stage of L2 acquisition and direct access to concepts after L2 proficiency is achieved. However, the model is not well supported by subsequent empirical evidence, and encounters difficulty in explaining cross-language priming data. The recently developed Sense Model (Finkbeiner, M., Forster, K., Nicol, J., & Nakamura, K., 2004) assumes a direct access from the L2 form to its related meaning and argues for the representational asymmetry in lexical semantics between L1 and L2. This model was designed to account for the translation asymmetry and task effect in the masked priming literature: L2-L1 priming is not observed in lexical decision due to the small proportion of L1 senses activated by the L2 prime; however, the category provides a context which restricts L1 sense activation and thus enhances the effectiveness of the L2 prime in semantic categorization. This dissertation reports the results of several semantic categorization experiments designed to test several assumptions of the Sense Model. Experiments 1-4 investigated whether the Category Restriction Hypothesis assumed by the Sense Model was empirically supported when congruence effects are minimized. The results showed that translation priming could be obtained for exemplars when congruence effects were controlled, but that there were no effects for non-exemplars, as predicted by the Sense Model. Subsequent experiments showed that category size is an important variable, since L2-L1 priming was not obtained with large categories (e.g., living thing), which was taken to indicate that a large category is ineffective as a 'focusing' device to enhance the activation of L2 semantic senses. Finally, it was shown that the priming asymmetry in lexical decision was not due to differential degrees of semantic activation of the prime in L1 and L2.

Dans ce travail, nous étudions les mécanismes du changement de langue lors de la reconnaissance visuelle de mots chez des trilingues français /anglais /espagnol. Dans un premier temps, nous avons examiné les processus d’accès pour chacune des langues étudiées, indépendamment de la présentation des autres langues. Nous nous sommes ensuite interrogés sur les relations entre les langues et l’organisation lexicale sous-jacente dans la mémoire multilingue, ainsi que la mise en place des mécanismes cognitifs permettant de passer d’une langue à une autre. Dans cette perspective, nous avons réalisé trois séries d’expériences afin d’examiner l’influence mutuelle des langues et le coût cognitif consécutif à un changement de langue lors de la reconnaissance visuelle de mots isolés. Nous avons comparé le traitement de mots spécifiques à différentes langues (ayant un degré de recouvrement orthographique minimal) en faisant varier les situations de changement et en recueillant des données comportementales et chronométriques dans des tâches de décision lexicale, de catégorisation sémantique et d’amorçage sémantique par traduction. Les résultats mettent en évidence un ralentissement global du traitement dû au changement pour les trois langues. Nous avons également observé un coût cognitif suite à un changement de langue pour les trois langues, mais plus important lorsqu’il s’opère entre les deux langues les moins maîtrisées (L2 vers L3 et L3 vers L2). Les données obtenues confirment l’hypothèse d’unités lexicales intégrées au sein d’un même lexique dans la mémoire multilingue. Les résultats sont interprétés dans leur ensemble dans le cadre des principaux modèles de la mémoire bilingue/multilingue. / The present work focuses on language switching mechanisms during visual word recognition in French / English / Spanish trilinguals. First, we examined access to processing for each language, independently from the presentation of other languages. Then, our concern was to determine the different relations between languages and the underlying lexical organization inside the multilingual memory, as well as the activation of cognitive mechanisms allowing language switching. With this goal in mind, we performed three series of experiments to examine the influences between the languages, and the cognitive cost subsequent to a language switching during visual word recognition. We compare the processing of non-cognate words belonging to the three languages, manipulating the language switching situations and recording behavioral and electrophysiological data during lexical decision, semantic categorization and semantic translation priming. Results of these experiments highlight a general slowdown of processing consecutive to a language switch for all languages. Moreover, we observed a cognitive cost related to language switching for all the three languages, but bilaterally larger when it concerns the two non-dominant languages (L2 to L3 and L3 to L2). The recording data confirms the hypothesis of lexical representations integrated into a shared lexicon of multilingual memory. The results are interpreted in the light of the main models accounting for bilingual memory.