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Background: Verbal fluency tasks are routinely used in clinical assessment and research studies of aphasia. People with aphasia produce fewer items in verbal fluency tasks. It remains unclear if their output is limited solely by their lexical difficulties and/or has a basis in their executive control abilities. Recent research has illustrated that detailed characterization of verbal fluency performance using temporal characteristics of words retrieved, clustering and switching, and pause durations, along with separate measures of executive control stands to inform our understanding of the lexical and cognitive underpinnings of verbal fluency in aphasia. Aims: To determine the locus of the verbal fluency difficulties in aphasia, we compared semantic and letter fluency trials between people with aphasia and healthy control participants using a wide range of variables to capture the performance between the two groups. The groups were also tested on separate measures of executive control to determine the relationship amongst these tasks and fluency performance. Methods & Procedures: Semantic (animal) and letter (F, A, S) fluency data for 60s trials were collected from 14 people with aphasia (PWA) and 24 healthy adult controls (HC). Variables, such as number of correct responses, clustering and switching analyses, were performed along with temporal measures of the retrieved words (response latencies) and pause durations. Participants performed executive control tasks to measure inhibitory control, mental‐set shifting and memory span. Outcomes & Results: Compared with HC, PWA produced fewer correct responses, showed greater difficulty with the letter fluency condition, were slower in getting started with the trials, showed slower retrieval times as noted in within‐ and between‐cluster pause durations, and switched less often. Despite these retrieval difficulties, PWA showed a similar decline in the rate of recall to HC, and had similar cluster size. Executive control measures correlated primarily with the letter fluency variables: mostly for PWA and in one instance for HC. Conclusions & Implications: Poorer performance for PWA is a combination of difficulties in both the lexical and executive components of the verbal fluency task. Our findings highlight the importance of detailed characterization of fluency performance in deciphering the underlying mechanism of retrieval difficulties in aphasia, and illustrate the importance of using letter fluency trials to tap into executive control processes. WHAT THIS PAPER ADDS: What is already known on the subject: PWA typically show impaired performance in verbal fluency tasks. It is debated whether this impaired performance is a result of their lexical difficulties or executive control difficulties, or a combination of both. This debate continues because previous studies have mostly used semantic fluency condition without including letter fluency condition; used a limited range of variables (e.g., number of correct responses); and not included separate executive control measures to explain the performance pattern in aphasia. This research addresses these outstanding issues to determine the specific contribution of lexical and executive control processes in verbal fluency in aphasia by including: both semantic and letter fluency conditions; a wide range of variables to identify the relative contribution of lexical and executive control mechanisms; and independent measures of executive control. What this paper adds to existing knowledge: Using the multidimensional analysis approach for verbal fluency performance from both semantic and letter fluency conditions, this is the first study to systematically demonstrate that PWA had difficulties in both lexical and executive control components of the task. At the individual level, PWA had greater difficulty on the letter fluency condition compared with semantic fluency. We observed significant correlations between the executive control measures and verbal fluency measures primarily for the letter fluency condition. This research makes a significant contribution to our understanding of lexical and executive control aspects in word production in aphasia. What are the potential or actual clinical implications of this work?: From a clinical perspective, this research highlights the importance of using a full range of verbal fluency and executive control measures to tap into the lexical as well as executive control abilities of PWA, and also the utility of using letter fluency to tap into the executive control processes in PWA. [ABSTRACT FROM AUTHOR]

Most models of word production converge on the assumption that selecting a specific word to name is a competitive process. Monolingual speakers experience lexical competition in their spoken language (i.e., within-language competition), but bilingual speakers who constantly juggle two sets of lexical items face within- and between-language competition. It has been argued that one of the reasons bilingual speakers perform poorly in linguistic tasks compared to monolinguals is the interference from the non-target language. However, this constant juggling of two languages has also been proposed to lead to better executive control abilities in bilinguals. The aim of this research was to determine the relationship between increased lexical competition as induced by semantic context manipulation in the blocked-cyclic picture naming paradigm, and executive control processes in bilingual and monolingual speakers. We implemented the blocked-cyclic picture naming paradigm to induce increased lexical competition and employed independent executive control tasks to understand its role in reducing increased lexical competition. We also computed delta plots – size of interference effects as a function of naming latencies – to investigate the type of inhibition involved in the blocked-cyclic picture naming paradigm. In this paradigm, objects to be named were presented in close succession, either from the same semantic categories (homogeneous: elephant, lion, deer, tiger, and cat) or different ones (heterogeneous: pear, shoes, lips, saw, and deer). Naming latencies are longer in the homogeneous context due to the heightened activation of competitors, and the difference in latencies between the homogeneous and heterogeneous contexts is referred to as semantic context effect. The participants were 25 young, healthy Bengali-English bilinguals and 25 healthy, age-, gender- and education-matched English monolinguals. All participants performed a blocked-cyclic naming task in English as well as three independent executive control tasks, tapping into their inhibitory control (Stroop task), mental-set shifting (colour-shape switch task), and working memory (backward digit span task). The key group differences were as follows: bilinguals showed less semantic context effect and more semantic facilitation on the first presentation cycle, applied more selective inhibition in both blocked-cyclic picture naming and Stroop tasks as measured by delta plots, showed better inhibitory control (Stroop task) and shifting abilities, but showed comparable working memory span. The correlation findings for both groups were as follows: slope of the slowest delta segment correlated with the magnitude of the semantic context effect in the blocked-cyclic naming task, no correlation between the slope and interference effect in the Stroop task, no correlation between slope of the two tasks, and no correlations between the semantic context effect with any of the measures derived from the independent executive control tasks. This is the first study to establish that bilinguals are less affected by semantic context manipulation and show a reduced interference effect for the longest naming latencies, compared to monolinguals. It also illustrates that even in a challenging linguistic task that heightens lexical competition, bilinguals performed better than monolinguals. This challenges the notion that bilinguals are disadvantaged compared to monolinguals in linguistic tasks, and we conclude that this study provides evidence for the advantage of bilingualism in linguistic tasks where executive control demands are higher. • The semantic context effects between bilinguals and monolinguals were explored on a blocked-cyclic picture naming task. • The type of inhibition was computed using delta plots for the blocked-cyclic picture naming task and Stroop task. • Bilinguals showed smaller semantic context effect, and larger semantic facilitation during first presentation cycle. • Bilinguals applied more selective inhibition in both blocked-cyclic picture naming and Stroop tasks. • The findings challenge the notion that bilinguals are disadvantaged compared to monolinguals in linguistic tasks. [ABSTRACT FROM AUTHOR]