Examining the Consequences of Phonological Impairment in Aphasia, Alexia, and Agraphia

Abstract

Background: The most common cause of aphasia is a left middle cerebral artery stroke affecting the left perisylvian region of the brain. The perisylvian region is critical for supporting phonological processing, and damage to this region results in difficulty with retrieving and manipulating speech sounds. The impact of weakened phonology has been well-documented in the context of the written language profiles of phonological alexia and agraphia, where there is disproportionate difficulty with reading and spelling nonwords (e.g., “plint”) compared to real words (Beauvois & Dérouesné, 1979; Shallice, 1981). The consequences of phonological impairment are also relevant in relation to everyday reading and writing. Specifically, Friedman (1996) and Beeson and colleagues (2018) documented markedly impaired grammatical performance in text-level reading and writing in individuals with phonological impairment; however, there is limited detail regarding the nature of these impairments. The present study aimed to examine sentence-level reading and writing abilities in individuals with a range of phonological skill. Methods: Twenty individuals with aphasia due to left hemisphere stroke and 10 neurotypical controls participated in this study. All participants completed a comprehensive language assessment battery to characterize the status of underlying central cognitive processes and peripheral sensorimotor skills that support spoken and written language. For this study, we developed a novel structured sentence task to measure sentence-level performance in oral reading, repetition, and writing, as well as evaluate the relative vulnerability of different word types (e.g., content vs. function vs. inflectional markers). This novel task allowed comparison of both reading and writing relative to clear and consistent targets. Results: Our cohort with aphasia demonstrated a marked impairment of phonological skill with mild-to-moderate spoken language deficits and relatively preserved semantic processing. In our cohort of 20 individuals with aphasia, 15 had phonological alexia and 12 had phonological agraphia. At the sentence level, we noted significant impairment of inflectional morphemes relative to content words. This “morphological” effect was significant for 7 individuals in sentence reading (phonological text alexia) and 8 in sentence writing (phonological text agraphia). The contribution of phonology to written sentence performance was further affirmed by a series of linear regression models in which phonological skill emerged as a significant predictor of overall written sentence accuracy on the structured sentence task, as well as the accurate use of inflectional markers in written sentences. Conclusion: This was one of the first studies to directly compare sentence reading and writing performance in the same cohort of individuals with aphasia due to left perisylvian damage. Our findings demonstrate the relative vulnerability of function words and inflectional markers in sentence- and paragraph-level written language associated with the common profile of weakened phonological skill. Future research is warranted to further clarify the nature of sentence-level written difficulty relative to phonological impairment. Additionally, these findings endorse the potential benefit of directing treatment toward the underlying impairment to maximize remediation of written language in individuals with aphasia.