Learning ability in post-stroke aphasia : success, strategy use and implications for therapy

Abstract

Aphasia is an impairment in the expression or comprehension of language that results from stroke, traumatic brain injury or progressive neurological disease. Approximately one million people in the United States suffer from aphasia, with the prevalence projected to increase to two million by 2020. Research has shown that speech-language therapy, the treatment for aphasia, can significantly improve people's ability to communicate. However, a major limitation in the field of aphasia rehabilitation is the lack of predictability in patients' response to therapy and the inability to tailor treatment to individuals. We hypothesize that learning represents a critical, underexplored factor in aphasia rehabilitation. Predicting whether a patient will improve following therapy may depend more upon that individual's ability to learn new information in general than upon a specific ability to relearn and master language. In this thesis I report a series of experiments that introduce a new approach that looks beyond language, proposing that the answer to developing efficacious, individually tailored therapies lies in a better understanding of the mechanisms of nonverbal learning in individuals with aphasia. We first explore learning success on a test of nonlinguistic category learning to examine whether learning differences arise among individuals with aphasia and non-aphasic controls. In Experiment 2, we probe the impact of stimulus manipulations on learning success. Experiment 3 presents an investigation into the relationship between learning score and language therapy outcomes. Finally, in Experiment 4, we examine the strategies used to perform our task in order to better understand how information is processed during probabilistic category learning. Results support the hypothesis that aphasia differentially affects language and learning networks. Instruction method and stimulus complexity were found to impact learning success and strategy use in individuals with aphasia. Furthermore, a positive correlation was found between learning scores and success with language therapy, suggesting that there is an informative relationship between learning ability and therapy outcomes. Findings draw attention to underlying processes that have not yet been the focus of research in aphasia, yet likely contribute to outcomes with therapy and present a gateway towards individualizing therapy and improving the predictability of patient outcomes.