| Περίληψη: | The present research investigates the processing of compound words in Primary Progressive Aphasia (PPA), amnestic Alzheimer’s disease (aAD), and behavioral Frontotemporal Dementia (bvFTD), neurodegenerative syndromes with prominent difficulties at the lexical level of language processing. Given that compounding fits within the realm of morphological and semantic processing, the study allowed us to investigate how these types of knowledge interact at the word level and how they affect lexical access in these distinct dementia populations. To this end, two offline production experiments and two online lexical decision tasks were conducted to investigate the explicit and implicit knowledge of compound words in both production and recognition modalities. The stimuli for these tasks included various types of compounds as well as pseudo-compounds, in order to examine the knowledge of people with dementia about the morphological structure of compound words and compound properties.
The findings of this research bring to light new data on the processing of morphologically complex, compound words in dementia populations. First, compounding posits greater production difficulties in PPA, aAD, and bvFTD syndromes compared to single words as opposed to healthy aging, suggesting that the knowledge about the compositional nature of a compound - structurally and semantically - is compromised in dementia. Second, PPA-S, PPA-NF/A, PPA-L, and bvFTD individuals were not able to detect violations of the compound structure (structural and morpho-semantic violations), indicating that the knowledge of the morphological status, structure, and rules of compounding is particularly compromised in PPA and bvFTD. Healthy elderly had significantly longer reaction times in pseudo-compounds than compounds, suggesting that morpho-semantic and characteristics of the compound structure are being processed during lexical access. Third, relational structure affects the performance of people with dementia, advocating the idea that it is an important determinant of the compound’s representation and processing. Fourth, semantic aspects of word knowledge are vulnerable in PPA-NF/A and PPA-L variants.
The current thesis has a psycho-/neurolinguistic and clinical contribution as it deals with aspects of lexical processing which have not been looked at in dementia research until now. The overall findings indicate that aspects of the morphological and semantic knowledge are affected by dementia regardless of whether the core language problem is semantic (PPA-S, aAD, bvFTD), phonological (PPA-L), or grammatical (PPA-NF/A). Thus, this research enriched our knowledge of the linguistic profile of PPA, aAD, and bvFTD. The performance of people with dementia is consistent with an approach that a large-scale network supports lexical processing and could be disturbed in dementia irrespective of whether the profound clinical symptom is in the language (PPA-S, PPA-NF/A, PPA-L), memory (aAD), or behavior (bvFTD), notwithstanding this network could be disturbed partially distinct.
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