Positive relationship between cognitive function and language performance over the course of conversation therapy targeting functional communication in people with aphasia : an initial study

Abstract

There has been a growing interest in studying the role of cognitive functions in language processing and rehabilitation of people with aphasia (PWA). Associations between cognitive components and various language tasks have been reported and proposals of the roles of different cognitive domains in explaining patterns of language performance/deficits have been offered. Specifically, cognitive functions such as executive functions (EF) and working memory are found to be predictive of treatment gains in naming therapy. However, issues concerning the patterns of associations of cognitive functioning and multi-level linguistic processing, the role of cognition in rehabilitation of functional communication, and more importantly, whether treatment-induced improvements in cognition may further benefit language gain, remain unclear. The present study aims to investigate these issues by comparing the outcomes of two treatment protocols on cognition and language, and examining their patterns of associations over the course of therapy. The performance of 53 Cantonese-speaking PWA in an array of cognitive tasks reflecting EF, attention, and verbal short-term and working memory was evaluated. Principal component analysis was conducted on the dataset and two cognitive factors were extracted, namely attention and memory, and EF, which were subsequently entered in multiple regression analyses to predict PWA’s performance in word comprehension and production, sentence comprehension, and discourse production. Differential patterns of associations between cognitive and linguistic processing were found. EF significantly predicted performance in word comprehension and production, sentence comprehension and most of the discourse production tasks with increasing level of importance as a function of linguistic complexity, whereas attention and memory primarily predicted PWA’s performance in word comprehension and production. From the initial group of PWA participants, 24 of them completed a novel treatment protocol comprising 12 sessions of cognitive stimulation plus conversation coaching, while another 23 participants received conversation therapy only. Their performance in primary and secondary language outcomes, together with possible changes in the two cognitive factors, were monitored throughout the course of therapy. Concurrent with the research hypothesis, baseline performance in EF did not predict treatment gains in functional communication. However, contrary to expectation, gains in cognitive performance and functional communication were observed in both treatment groups to similar extent. Maintenance of treatment effects was present in functional communication and EF but absent in the cognitive factor representing attention and memory. In addition, different patterns of relationships were found between cognitive and language domains over the course of treatment. The main findings of the study support the views about the interactive nature of cognitive and language domains, and that processing of linguistic tasks of varying degrees of complexity are differentially sub-served by different cognitive functions. The importance of EF is demonstrated in language processing and rehabilitation of functional communication, which further emphasizes the significance of cognitive evaluation in clinical management of PWA. Treatment-induced improvements in cognitive and linguistic performance are attributed to the meta-cognitive, explicit, goal-directed, interactive and naturalistic nature of conversation coaching. Possible explanations for the null effect of cognitive stimulation are considered and future studies regarding cognitive and rehabilitation of neurogenic communication disorders are proposed.