Double-Dissociation in Noun and Verb Production in Bilingual Aphasia

• ¹ University of Reading, School of Psychology and Clinical Language Sciences, United Kingdom
• ² University of Reading, Institute of Education, United Kingdom

Introduction: Language impairments exhibited in bilingual aphasia are often manifested differentially in the two languages (Abuom & Bastiaanse, 2012; Fabbro, 2001; Faroqi-Shah & Waked, 2010). For example, verb production was inferior to nouns in three languages of a trilingual individual with aphasia (Faroqi-Shah & Waked, 2010). Although dissociations in grammatical class in aphasia is well-documented (e.g., verbsVerbs; Hindi Verbs>Nouns, Balasubramanian & Bose, 2016). In this research, we further examined this noun-verb dissociation by using single-word production tasks (i.e., picture naming and repetition). Our goal was to establish whether the double-dissociation evidenced in the narrative task was a strategy employed in a relatively unstructured task (i.e., connected speech) with fewer restrictions or if he indeed had specific and differential difficulty in retrieving nouns and verbs of each language. Participant profile: RZ was a 32 -year old right-handed, highly educated man with an engineering degree. He was five years post-onset to a severe traumatic brain injury. At the time of this research, he was mobile but experienced continued hemiplegia. Pre-injury RZ was equally proficient in both Hindi and English. Post-onset he primarily used Hindi for verbal communication and English for telecommunication. RZ exhibited moderate Broca’s aphasia in both languages. We also collected data from an age, gender and education-matched healthy bilingual control individual (BC) for comparison. Tasks: A narrative sample was elicited using the Frog story (Mayer, 1969) in the bilingual mode (i.e., no restriction was placed on the language of choice for the narrative production). Narrative words including nouns and verbs were extracted using the Quantitative Production Analysis protocol (Berndt et al, 2000). For the naming and repetition task, we used 30 nouns and 24 verbs for the task developed by Venkatesh et al (2012). These tasks were tested in English and Hindi on separate days. Responses on single-word production tasks were analysed for accuracy and error types. Results & Discussion: Figure 1 illustrates the noun and verb performance across tasks in both languages. RZ’s noun-verb repetition was unimpaired suggesting that when the phonological form was available to him, he could retrieve and repeat accurately. However, on the narrative task, RZ exhibited a noun-verb double-dissociation (Hindi: verbs >nouns; English: nouns>verbs). This pattern was also evident in the picture naming task (i.e., Hindi: verbs >nouns; English: nouns>verbs), suggesting differential grammatical class impairment in each language. Possible reason for this could be separate grammatical category storage for each language (Faroqi-Shah & Waked, 2010). These findings challenge the notion that nouns and verbs have shared neural representations (Abutalebi, 2008), specially from typologically distinct languages (in this case Hindi and English) and for diffused brain lesion such as in traumatic brain injury.