Verbal fluency in bilingual Lebanese adults: Is the prominent language advantage due to executive processes, language processes, or both?

Although bilingualism is widespread, little data on verbal fluency tasks (VFTs) within bilingualism subtypes and the underlying mechanisms exist. The study's objective was to explore executive and language processes in 10 semantic and letter VFTs and a set of language and executive tests among 100 elderly Arabic-French bilinguals from three bilingualism subgroups: Arabic-dominant, French-dominant, and balanced. We observed a prominent-language advantage for semantic and letter VFTs in French but not for letter VFTs in Arabic. This advantage in the VFT was associated with a sustained rate of late production, a higher percentage of specific words, a higher number of clusters, and a larger cluster size, and was related mainly to language processes. Our results suggest that the strategic search processes underlying VFTs operate on the two phonological output lexicons of bilinguals with similar characteristics in different languages and thus support the hypothesis of a single, centralized, strategic search process.

Functional architecture of executive processes: Evidence from verbal fluency and lesion mapping in stroke patients.

The functional organization and related anatomy of executive functions are still largely unknown and were examined in the present study using a verbal fluency task. The objective of this study was to determine the cognitive architecture of a fluency task and related voxelwise anatomy in the GRECogVASC cohort and fMRI based meta-analytical data. First, we proposed a model of verbal fluency in which two control processes, lexico-semantic strategic search process and attention process, interact with semantic and lexico-phonological output processes. This model was assessed by testing 404 patients and 775 controls for semantic and letter fluency, naming, and processing speed (Trail Making test part A). Regression (R2 = .276 and .3, P = .0001, both) and structural equation modeling (CFI: .88, RMSEA: .2, SRMR: .1) analyses supported this model. Second, voxelwise lesion-symptom mapping and disconnectome analyses demonstrated fluency to be associated with left lesions of the pars opercularis, lenticular nucleus, insula, temporopolar region, and a large number of tracts. In addition, a single dissociation showed specific association of letter fluency with the pars triangularis of F3. Disconnectome mapping showed the additional role of disconnection of left frontal gyri and thalamus. By contrast, these analyses did not identify voxels specifically associated with lexico-phonological search processes. Third, meta-analytic fMRI data (based on 72 studies) strikingly matched all structures identified by the lesion approach. These results support our modeling of the functional architecture of verbal fluency based on two control processes (strategic search and attention) operating on semantic and lexico-phonologic output processes. Multivariate analysis supports the prominent role of the temporopolar area (BA 38) in semantic fluency and the F3 triangularis area (BA 45) in letter fluency. Finally, the lack of voxels specifically dedicated to strategic search processes could be due to a distributed organization of executive functions warranting further studies.