Lexical and Cognitive Underpinnings of Verbal Fluency: Evidence from Bengali-English Bilingual Aphasia

Abstract

Research in bilingual healthy controls (BHC) has illustrated that detailed characterization of verbal fluency along with separate measures of executive control stand to inform our understanding of the lexical and cognitive underpinnings of the task. Such data are currently lacking in bilinguals with aphasia (BWA). We aimed to compare the characteristics of verbal fluency performance (semantic, letter) in Bengali–English BWA and BHC, in terms of cross-linguistic differences, variation on the parameters of bilingualism, and cognitive underpinnings. BWA showed significant differences on verbal fluency variables where executive control demands were higher (fluency difference score, number of switches, between-cluster pauses); whilst performed similarly on variables where executive control demands were lower (cluster size, within-cluster pauses). Despite clear cross-linguistic advantage in Bengali for BHC, no cross-linguistic differences were noted in BWA. BWA who were most affected in the independent executive control measures also showed greater impairment in letter fluency condition. Correlation analyses revealed a significant relationship for BWA between inhibitory control and number of correct responses, initial retrieval time, and number of switches. This research contributes to the debate of underlying mechanisms of word retrieval deficits in aphasia, and adds to the nascent literature of BWA in South Asian languages.

Clustering and Switching in Verbal Fluency Across Varying Degrees of Cognitive Control Demands: Evidence From Healthy Bilinguals and Bilingual Patients With Aphasia

“…Given that letter fluency is thought to have higher cognitive control demands while semantic category generation is thought to place greater emphasis on lexico-semantic abilities ( Luo et al, 2010 ; Patra et al, 2020b ; Shao et al, 2014 ), a smaller FDS is thought to be indicative of better cognitive control abilities ( Friesen et al, 2015 ; Patra et al, 2020b ). A recent study by Patra et al (2020b) found that BPWA produced fewer correct words, had larger FDSs, and switched fewer times as compared to healthy bilinguals; however, both groups demonstrated similar cluster scores. Additionally, they found that BPWA with better inhibitory control produced more correct words and a greater number of semantic switches, further supporting the role of cognitive control in switching performance.…”

“…Within the context of verbal fluency tasks, which has been extensively studied in bilingual individuals ( Friesen et al, 2015 ; Kiran et al, 2014 ; Luo et al, 2010 ; Patra et al, 2020a ; Roberts & Le Dorze, 1998 ) and is the focus of the current study, the ACH provides a framework to predict the influence of interactional contexts on the degree of control mechanisms required to successfully complete the task ( Carpenter et al, 2020 ; Jevtovic et al, 2020 ). Within this framework, we can examine two levels of control in bilingual speakers.…”

“…Recent studies have used a fluency difference score (FDS) as a measure of cognitive control ability in verbal fluency tasks ( Friesen et al, 2015 ; Patra et al, 2020a ). FDS is calculated by taking the difference in performance between the category generation and letter fluency tasks as a proportion of correct responses on the category generation task.…”

“… How does switching and clustering performance differ for BPWA and healthy bilinguals across the different conditions of the semantic category generation task? Given the findings of previous research ( Kiran et al, 2014 ; Patra et al, 2020a ), it was hypothesized that healthy bilinguals would produce larger mean semantic cluster sizes and a greater number of switches compared to BPWA, reflective of varying degrees of language impairment in the BPWA group. When looking at performance across conditions, we anticipated that clustering performance would be comparable across the four conditions for both groups as it is a measure of automatic spreading activation and should therefore be minimally impacted by increasing language control demands.…”

Connected Speech Characteristics of Bengali Speakers With Alzheimer's Disease: Evidence for Language-Specific Diagnostic Markers

“…Bengali is currently ranked as the seventh most spoken language in the world; more than 265 million people speak Bengali as their first or second language in their everyday life. Despite the large number of Bengali speakers there are only handful of studies involving Bengali speakers with neurological impairments (e.g., Lahiri et al, 2019 ; Patra et al, 2020 ), and remains one of the under-represented and under-explored world languages in neurological research (Beveridge and Bak, 2011 ).…”