Syntactic complexity does not affect verbal working memory capacity in non-fluent variant PPA

• ¹ Aristotle University of Thessaloniki, Department of English Studies, Greece
• ² University of Cambridge, Department of Theoretical and Applied Linguistics, United Kingdom
• ³ Johns Hopkins Medicine, Department of Neurology, United States

Introduction. There is extensive evidence showing dysfunction in the executive abilities of individuals with traumatic brain injury or with lesions to the (pre)frontal areas using tasks based on response conflict and working memory (e.g. Christensen & Wright, 2010; Lê et al. 2012; Riès et al., 2013). A crucial aspect of these studies is that the tasks used were non-verbal measures of attention and control and bore no obvious connection to language processing. The present study investigates the interaction between verbal working memory and syntactic processing in 8 patients with non-fluent variant Primary Progressive Aphasia (nfv-PPA) along with age- and education-matched healthy controls. Method. Eight individuals with nfv-PPA (Mean age: 65;8 yrs, SD: 4.6); Mean education in years: 15;4, SD: 2.2) and their neurologically-intact matched peers were administered two language tasks. In the first syntactic comprehension task, participants listened to sentences of varying structural complexity (i.e. transitives, subject relatives, passives, object relatives) while they were shown pictures on the screen. After sentence presentation, participants selected the picture matching the sentence. Along with syntactic comprehension tested through sentence-picture matching (SPM), participants had to remember intervening single word items that they had to recall after a block of four SPM trials (see example below). The second task was modeled after the proactive interference (PI) paradigm, in which participants were asked to recall the words from consecutive lists sharing category membership (Bialystok & Feng, 2009). 1st SPMT: The bike follows the bus (transitive) 1st word to be recalled: boot 2nd SPMT: The dog is bitten by the cat (passive) 2nd word to be recalled: clock 3rd SPMT: The lady that kisses the man pushes the girl (subject relative) 3rd word to be recalled: nose 4th SPMT: The girl that the young man kicks hugs the child (object relative) 4th word to be recalled: milk Results. In the syntactic comprehension task, both SPM accuracy and word-recall scores were calculated. On the word-recall measure, controls showed a significant Syntactic Complexity effect (F(3, 21)=3.124, p=.05), with word-recall being more erroneous after processing passives and object relatives (versus transitives and subject relatives). Contrary, the nfv-PPA group did not show an effect of syntactic complexity on word-recall (F(3, 21)=.612, p=.615), while they exhibited overall lower syntactic comprehension (F(1, 15)=20.660, p<.001) and word recall accuracy (F(1, 15)=12.943, p=.003) than controls. In the PI task, the nfv-PPA group’s retrieval of recent material did not appear to be impaired by prior exposure to similar items (F(2, 14)=.273, p=.765), in contrast to controls who have experienced significant interference effects (F(2, 14)=5.361, p=.02) created by the PI paradigm. Conclusions. The results from the syntactic comprehension task show that the nfv-PPA group was more impaired than controls in syntactic comprehension, yet, such impairment did not seem to affect their word-recall capacity which was weaker relative to controls across all four sentence-types. In the PI task, the nfv-PPA group did not show a significant decline in recall across lists, indicating lack of normal interference from previously-presented material. Overall, the lack of verbal interference attested in both tasks suggests that syntactic processing and WM in individuals with nfv-PPA may not draw on the same processing resources. References Bialystok, E., & Feng, X. (2009). Language proficiency and executive control in proactive interference: Evidence from monolingual and bilingual children and adults. Brain & Language, 109, 93-100. Christensen, S. C., & Wright, H. H. (2010). Verbal and non-verbal working memory in aphasia: What three n-back tasks reveal. Aphasiology, 24 , 752-762. Ivanova, M., Dragoya, O. V., Kuptsova, S. V., Ulicheva, A. S., & Laurinavichyute, A. K. (2014). The contribution of working memory to language comprehension: differential effect of aphasia type. Aphasiology, 29, 645-664. Lê, K., Coelho, C., Mozeiko, J., Krueger, F. & Grafman, J. (2012). Predicting Story Goodness Performance From Cognitive Measures Following Traumatic Brain Injury. American Journal of Speech & Language Patholology, 21, 115-125. Riès, S., Xie, K., Haaland, K. Y., Dronkers, N. F., & Knight, R. T. (2013). Role of the lateral prefrontal cortex in speech monitoring. Frontiers in Human Neuroscience, 7, 703. doi: 10.3389/fnhum.2013.00703.