The relationship between non-orthographic language abilities and reading performance: An exploration of the primary systems hypothesis in chronic aphasia

Thesis (Ph.D.)--University of Washington, 2016-06

Individuals with aphasia, an acquired language processing disorder, commonly present with both spoken (i.e., language production and comprehension) and written (i.e., reading and spelling) language impairments. Traditionally, spoken and written language have been assumed to rely on distinct linguistic representations and processing mechanisms. Alternatively, the primary systems hypothesis, which is grounded in parallel-distributed processing theory, proposes written language abilities developed from and are reliant on the same primary brain systems that support spoken language. Therefore, the primary systems hypothesis postulates all language activities, including naming, reading, and spelling, are supported by an interconnected language system. Empirical support for this hypothesis is promising, yet limited, and therefore these claims remain controversial. Motivated by the primary systems hypothesis, the purpose of this study was to examine the relationship between non-orthographic (i.e., no letters) spoken language abilities and written language abilities, specifically reading performance, in aphasia. Forty-three individuals with chronic, left-hemisphere stroke-induced aphasia participated in the study. Performance on non-orthographic semantic, phonologic, and syntactic tasks, as well as performance on oral reading and silent reading comprehension tasks was assessed and analyzed. Specifically, Pearson correlations were calculated to determine the size and strength of the associations between non-orthographic language abilities and reading abilities. Additionally, non-orthographic language composite scores were entered as predictors of reading performance in multiple linear regression models. Lastly, a reading profile (i.e., surface, phonological, deep, global alexia or within normal limits) was determined for each participant based on oral reading accuracy and types of reading errors produced. Then, the relationship between degree of semantic and phonologic impairment and type of acquired reading impairment (i.e., alexia) was examined. Results showed that non-orthographic language abilities were statistically significantly related to oral reading and silent reading comprehension abilities, as well as alexia subtype, in this diverse sample of individuals with aphasia. In regard to oral reading ability, semantic abilities were found to be most predictive of regular and irregular word reading, while phonologic abilities were most predictive of pseudohomophone and nonword reading. The silent reading comprehension analyses revealed written word and written paragraph comprehension were primarily supported by semantics. Whereas, written sentence comprehension was significantly related to semantic, phonologic, and syntactic performance, with the strongest association with syntax. Finally, severity of alexia was found to reflect severity of semantic and phonologic impairment. The results of this work offer promising support for the primary systems view of language processing by showing non-orthographic language abilities are closely linked to oral reading and silent reading comprehension performance in chronic aphasia. Additionally, the data suggest alexia subtype in aphasia can be described based on non-orthographic semantic and phonologic performance. This finding further endorses the primary systems notion that alexia stems from an underlying general language, as opposed to reading-specific, impairment. Moreover, this work clinically suggests that assessing and treating non-orthographic semantic and phonologic abilities may be useful in alexia rehabilitation. These findings are preliminary, and therefore this work needs to be replicated and extended to further understand the connection between acquired spoken and written language impairments in aphasia.