Remediation of language processing in aphasia: Improving activation and maintenance of linguistic representations in (verbal) short-term memory

Background: Verbal short-term memory (STM) impairments are invariably present in aphasia. Word processing involves a minimal form of verbal STM, i.e., the time course over which semantic and phonological representations are activated and maintained until they are comprehended, produced, or repeated. Thus it is reasonable that impairments of word processing and verbal STM may co-occur. The co-occurrence of language and STM impairments in aphasia has motivated an active area of research that has revealed much about the relationship of these two systems and the effect of their impairment on language function and verbal learning (Freedman & Martin, 2001 Freedman, M. L. and R. Martin, R. C. 2001. Dissociable components of short-term memory and their relation to long-term learning. Cognitive Neuropsychology, 18: 193–226. [Taylor & Francis Online], [Web of Science ®] , [Google Scholar]; Martin & Saffran, 1999 Martin, N. and Saffran, E.M. 1999. Effects of word processing and short-term memory deficits on verbal learning: Evidence from aphasia. International Journal of Psychology, 34(5/6): 330–346. [Web of Science ®] , [Google Scholar]; Trojano & Grossi, 1995 Trojano, L. and Grossi, D. 1995. Phonological and lexical coding in verbal short-term-memory and learning. Brain and Language, 51(2): 336–354.  [Google Scholar]). In keeping with this view a number of researchers have developed treatment protocols to improve verbal STM in order to improve language function (e.g., Koenig-Bruhin & Studer-Eichenberger, 2007 Koenig-Bruhin, M. and Studer-Eichenberger, F. 2007. Therapy of verbal short-term memory disorders in fluent aphasia: A single case study. Aphasiology, 21(5): 448–458. [Taylor & Francis Online], [Web of Science ®] , [Google Scholar]). This account of aphasia predicts that treatment of a fundamental ability, such as STM, which supports language function, should lead to improvements that generalise to content and tasks beyond those implemented in treatment.

Aims: We investigated the efficacy of a treatment for language impairment that targets two language support processes: verbal short-term memory (STM) and executive processing, in the context of a language task (repetition). We hypothesised that treatment of these abilities would improve repetition abilities and performance on other language tasks that require STM.

Method: A single-participant, multiple-baseline, multiple-probe design across behaviours was used with a participant with conduction aphasia. The treatment involved repetition of words and nonwords under three “interval” conditions, which varied the time between hearing and repeating the stimulus. Measures of treatment effects included acquisition, maintenance, and follow-up data, effect sizes, and pre- and post-treatment performance on a test battery that varies the STM and executive function demands of language tasks.

Outcomes & Results: Improvement of repetition was mostly specific to treated stimuli. Post-treatment measures of language ability indicated improvements in single and multiple word processing tasks, verbal working memory tasks, and verbal span.

Conclusions: Treatment of STM and executive processes in the context of a word repetition task resulted in improvements in other non-treated language tasks. The approach used in this study can be incorporated into other language-processing tasks typically used in treatment of language disorders (e.g., sentence processing).