Research Article the Nature of Lexical-Semantic Access in Bilingual Aphasia
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Hindawi Publishing Corporation Behavioural Neurology Volume 2014, Article ID 389565, 18 pages http://dx.doi.org/10.1155/2014/389565 Research Article The Nature of Lexical-Semantic Access in Bilingual Aphasia Swathi Kiran, Isabel Balachandran, and Jason Lucas Department of Speech Language and Hearing Sciences, Boston University Sargent College, 635 Commonwealth Avenue, Boston, MA 02215, USA Correspondence should be addressed to Swathi Kiran; [email protected] Received 25 January 2013; Accepted 29 September 2013; Published 30 March 2014 Academic Editor: Jubin Abutalebi Copyright © 2014 Swathi Kiran et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Background. Despite a growing clinical need, there are no clear guidelines on assessment of lexical access in the two languages in individuals with bilingual aphasia. Objective. In this study, we examined the influence of language proficiency on three tasks requiring lexical access in English and Spanish bilingual normal controls and in bilingual individuals with aphasia. Methods. 12 neurologically healthy Spanish-English bilinguals and 10 Spanish-English bilinguals with aphasia participated in the study. All participants completed three lexical retrieval tasks: two picture-naming tasks (BNT, BPNT) and a category generation (CG) task. Results. This study found that across all tasks, the greatest predictors for performance were the effect of group and language ability rating (LAR). Bilingual controls had a greater score or produced more correct responses than participants with bilingual aphasia across all tasks. The results of our study also indicate that normal controls and bilinguals with aphasia make similar types of errors in both English and Spanish and develop similar clustering strategies despite significant performance differences between the groups. Conclusions. Differences between bilingual patients and controls demonstrate a fundamental lexical retrieval deficit in bilingual individuals with aphasia, but one that is further influenced by language proficiency in the two languages. 1. Introduction theprevailingtheorysuggeststhatactivationflowsfrom the semantic system to the phonological system of both Naming deficits are a commonly acquired disorder, mani- languages simultaneously, indicating that lexical access is festing in all types of aphasia [1, 2]; however, we are still target language-nonspecific6 [ , 7]. Thus, targets in both unclear about the nature and mechanisms underlying lexical languages are potentially active subsequent to semantic processing deficits in monolingual and bilingual individ- activation, but through a process of competitive selection, uals with aphasia. Theories of normal bilingual language the target in the accurate language is ultimately produced. processing indicate variable degrees of overlap between the An alternate, but not necessarily contradictory hypothesis, two languages. For instance, the revised hierarchical model isthefactthatinorderforbilingualstoaccessthetarget (RHM; [3–5]) allows for language proficiency differences language, the nontarget language must be inhibited [8–10]. by proposing connections between both L1 and L2 and the In other words, a speaker activates target language lemmas semantic system; these connections differ in their strengths while simultaneously inhibiting the lemmas of the nontarget as a function of fluency in L1 relative to L2. In bilingual language. individuals with a dominant language, the lexicon of L1 There are several methods to examine lexical access in is generally assumed to be larger than that of L2 because bilingual individuals. The most common approach has been more words are known in the dominant language. Also, confrontation picture naming. In general, performance on lexical associations from L2 to L1 are assumed to be stronger picture naming tasks is constrained by the images presented than those from L1 to L2. Conversely, the links between the and influenced by word frequency and imageability. One semantic system and L1 are assumed to be stronger than such picture naming task that has been used extensively as a from the semantic system to L2. With regards to activation measure of lexical access in monolinguals and bilinguals is the of phonological representations from the semantic system, Boston Naming Test (BNT, [11]). For instance, Kohnert et al. 2 Behavioural Neurology [12] showed that normal young bilinguals performed better in ofwordsasbothEnglishandSpanishmonolinguals.There EnglishthanSpanishontheBNTandthatnamingaccuracy are other studies that have examined verbal fluency as a significantly correlated with self-ratings of language skills. measure of lexical-semantic access in bilingual individuals Similarly, Roberts et al. [13] examined naming on the BNT in other language combinations (e.g., Zulu/English, [26]; in French/English and Spanish/English bilinguals and found Finnish/English, [27]) and found differences in the degree that both bilingual groups scored significantly below the of performance across the two languages of the bilingual. To monolingual English group on the BNT. summarize, most studies examining category fluency in bilin- Another approach to examining lexical access includes gual individuals have demonstrated that participants tend to category generation verbal fluency tasks [14–17]. Verbal producemoreitemsinonelanguagerelativetoanotherand fluency has been found to be dependent on a multitude to task set (e.g., semantic or phonological cues), but no study of factors, including two qualitative features, clustering and has systematically examined the nature of category fluency switching ability. These strategic processes are mediated by in bilingual individuals across a set of semantic categories by executive functioning and verbal memory storage and have taking into account language proficiency. therefore been a successful predictor of lexical access ability Both lexical access tasks described above, picture naming [18, 19]. Performance on the task is highly contingent on and verbal fluency, test lexical access but in slightly different the success of the generation of semantically related words ways. In both tasks, the measure of lexical access theoretically in a subcategory, or clustering, which utilizes an individual’s involves parallel activation of both languages with highly language stores. There is also an equally essential component interactive phonological and semantic representations that of switching between subordinate categories in the verbal spread through the levels of language representation [6]. fluency task, which relies on an efficient cognitive flexibility However, sufficient crucial differences in the theoretical basis [20–22]. Therefore, simply examining the number of correct between the tasks exist to investigate different properties wordsisnotsufficienttounderstandtheperformanceonthe of lexical access. Performance on picture naming tasks is task [16]. constrained by the images presented, making nonlinguistic The nature of semantic organization in the two languages strategies like clustering and switching ineffective. Perfor- of a bilingual individual affects influences their performance mance on the picture naming tasks is driven mainly by word on verbal fluency tasks. For instance, Roberts and Le Dorze frequency and imageability. Also, categories in the category [23] examined category generation in French-English par- generation task have a certain degree of flexibility with regard ticipants and found that there was no language effect on to items that belong to a given category which is not present the number of correct responses across languages. However, in a picture naming task. On the verbal fluency task, however, for animals, French-English bilinguals recalled more subcate- nonlinguistic and semantically unrelated phonological strate- gories (birds, insects, etc.)inFrenchthanEnglish.Theauthors gies are effective means of performing the task. Grouping suggested that some semantic fields may have similar type clusters is dependent on the way semantically related words of semantic organization across languages, whereas others are organized in the brain. Clustering and switching abilities may differ between languages even in balanced bilinguals. on the verbal fluency task are dependent on individual The authors suggested that childhood experiences and the language exposure. The relative freedom of the category cultural environment play an important role in determining generation task (to semantically organize the categories) the nature of semantic system. also aids in the performance of the task by facilitating the In another set of studies, Rosselli et al. [24]firstcompared individual language abilities of the participants. Spanish-English bilinguals with English monolinguals and In contrast to studies on lexical access in nonbrain Spanish monolinguals on word fluency task using either damaged bilingual individuals, examination of lexical access phoneme letter cues or semantic categories. Results showed in bilingual aphasia is relatively sparse and most studies a lower performance in the bilingual participants compared are case studies of individuals with interesting but atypical to their monolingual counterparts on the semantic category language impairment profiles11 [ , 28–33]. In one group study, cued task but not on the phoneme letter cue task. They Tschirren et al. [34]