This thesis investigates the role of executive functions in language processing in primary progressive aphasia (PPA), with a particular focus on syntactic ambiguity resolution and narrative discourse production. The main aim was to determine whether language impairment in PPA can be explained as a purely linguistic deficit or as the result of an interaction between language-specific mechanisms and domain-general cognitive processes, such as executive functions. To address this question the study combined two complementary approaches. First, a behavioral self-paced reading paradigm was used to investigate the processing of garden path sentences in Greek. Second, an eye tracking case-series study provided fine-grained evidence of real-time processing mechanisms during temporary syntactic ambiguity resolution. Third, narrative production was examined across both oral and written modalities, by employing the following measures of microstructure: syntactic complexity, lexical diversity and proposition density, alongside executive function assessments. Narrative production was elicited through two paradigms: picture sequence and single picture description. The results indicate that persons with PPA (henceforth, PwPPA) exhibited reduced accuracy in garden path sentence comprehension, while no differences were found in corresponding reaction times. Eye tracking data further refined the pattern observed behaviorally: processing difficulty was predominantly found in disambiguation and post-disambiguation regions, thus reflecting the instability in maintaining and integrating revised representations in real-time. In narrative production, impairments were most pronounced in the oral modality in the conditions that required real-time sequencing. Notably, written performance was better in the PwPPA than their oral narrative production, while executive function measures predicted narrative production only selectively: more specifically, executive function measures predicted oral narrative performance only in sequenced pictures (vs. single picture description), while there were no associations between executive functions and written narrative production. The overall findings show that the written modality in narrative production reduces the load on the patients’ executive functions by alleviating real-time processing constraints. Overall, the findings support the account that language processing mechanisms interact with domain-general executive functions in PPA, particularly under conditions of increased cognitive demands such as those inflicted by temporary syntactic ambiguity and oral narrative production of picture sequences. Executive functions appear as key predictors of syntactic revision and narrative discourse organization. The thesis highlights the importance of combining both linguistic and cognitive factors in models of language processing and in the assessment of language impairment in PPA.
Βασιλίνα Ευάγγελου Σπανού (Thu,) studied this question.