Verbal working memory and its relationship to sentence‐level reading and listening comprehension in persons with aphasia

Abstract

Background: Working memory (WM) has gained recent attention as a cognitive construct that may account for language comprehension deficits in persons with aphasia (PWA) (Caspari, Parkinson, LaPointe, & Katz, 1998 Caspari, I., Parkinson, S. R., LaPointe, L. L. and Katz, R. C. 1998. Working memory and aphasia.. Brain and Cognition, 37: 205–223. [Crossref], [PubMed], [Web of Science ®] , [Google Scholar]; Martin, Kohen, & Kalinyak‐Fliszar, 2008 Martin, N., Kohen, F. and Kalinyak‐Fliszar, M. 2008. A diagnostic battery to assess language and short‐term memory deficits in aphasia Poster presentation at Clinical Aphasiology Conference, Teton Village, WY [Google Scholar]; Wright, Downey, Gravier, Love, & Shapiro, 2007 Wright, H. H., Downey, R. A., Gravier, M., Love, T. and Shapiro, L. P. 2007. Processing distinct linguistic information types in working memory in aphasia.. Aphasiology, 21: 802–813. [Taylor & Francis Online], [Web of Science ®] , [Google Scholar]). However, few studies have investigated individual differences in performance on sentence comprehension tasks as a function of WM capacity in PWA when WM demands are manipulated. Aims: The purposes of the current study were: (1) to examine the relationships among verbal WM, sentence comprehension, and severity of impairment in PWA and (2) to investigate the differential performance of high versus low verbal WM groups on sentence comprehension tasks in which task demands were manipulated by the length of the sentence stimuli, complexity of syntactic structure, and by presentation method which varied the time over which the linguistic material was available for computation. Methods & Procedures: A total of 20 PWA were divided into high and low WM groups based on a listening version of a WM sentence span task. Each participant completed a listening version (CRTT) and three reading versions (CRTT‐R) of the Computerised Revised Token Test as the sentence comprehension tasks. Outcomes & Results: The WM task significantly predicted performance on the CRTT conditions in which information was only temporarily available, thereby imposing greater WM demands on sentence comprehension. The verbal WM task was significantly correlated with aphasia severity and a principal components analysis revealed that the WM task, overall aphasia severity, and overall reading impairment level loaded on a single factor with 76% of shared variance. The low WM group's performance was significantly lower than the high WM group on the CRTT subtests with syntactically more complex structures and on the CRTT conditions with temporally restricted presentation methods. Conclusions: This verbal WM task was significantly and moderately correlated with the overall severity of aphasia as well as with both listening and reading sentence comprehension. The WM group differences emerged only in sentence comprehension tasks with greater WM demands. These results are consistent with the notion that WM effects are most evident when WM capacity is sufficiently taxed by the task demands (e.g., Caplan & Waters, 1999 Caplan, D. and Waters, G. S. 1999. Verbal working memory and sentence comprehension.. Behavioral and Brain Sciences, 22: 77–126. [Crossref], [PubMed], [Web of Science ®] , [Google Scholar]; Just & Carpenter, 1992 Just, M. A. and Carpenter, P. A. 1992. A capacity theory of comprehension: Individual differences in working memory.. Psychological Review, 99: 122–149. [Crossref], [PubMed], [Web of Science ®] , [Google Scholar]).