L’analyse du langage spontané comme outil de détection précoce du déclin cognitif : une approche écologique

Alzheimer's disease (AD) – the most common form of major neurocognitive disorder – is typically characterized by progressive and insidious impairment of episodic memory. Language deficits are also part of the clinical picture of the disease, and are already present in the preclinical stage of mild neurocognitive disorder (mild NCD). Difficulties in language production have been reported in AD and even in mild NCD, suggesting that its assessment may represent a unique opportunity for early detection of cognitive decline. There is a growing consensus that connected speech (CS) may provide an ecologically valid assessment of language production abilities. However, the results of studies that have examined CS assessment do not all converge to provide a clear picture of the impact of cognitive decline on language production in AD, and even less so in mild NCD.    The first part of the thesis thus aimed to comprehensively describe the extent of research in the area of CS assessment in AD and mild NCD populations, by conducting a scoping review (study 1). The results revealed that traditional CS assessment most often consisted of quantitative analysis of a selection of microlinguistic variables of CS, obtained using a standardized descriptive measure. Having replicated the pattern of language deficits widely found in the scientific literature, the results of the scoping review highlight the complementary contribution of CS assessment to the overall assessment of language in AD and mild NCD populations. However, the scoping review also highlighted important gaps in the research field, including the very few studies that have focused on mild NCD in comparison to AD, as well as the very few ecological approaches to CS assessment.  Taking these gaps into account, the second part of the thesis thus aimed to examine the contribution of a functional assessment of CS that is closer to the context of real life, with mild NCD participants and controls (study #2). More precisely, a functional assessment of the speech acts produced by these two groups during the performance of ecological tasks inspired by activities of daily living in a laboratory-apartment was carried out. Qualitative description of the speech acts spontaneously produced by these participants while performing complex tasks allowed for the extraction of distinct strategies, barriers and reactions in response to task demands as well as to the difficulties encountered by the mild NCD participants and controls. Thus, results showed that mild NCD participants implemented fewer proactive strategies before beginning the experiment, and then more compensatory strategies to support their task organization during task execution. More distracted and less likely to take into account the assistance offered, they validated and justified their performance more defensively and were more reactive to their difficulties than the control subjects. The results of the second article of the thesis thus highlight the innovative contribution of a functional assessment of CS as a tool for exploring the impact of cognitive decline in complex, ecological tasks that are similar to activities of daily living.  Together, the studies in this thesis converge to support the complementary contribution of a functional assessment of CS to its traditional assessment in advancing knowledge about the impact of cognitive decline on language production in the mild NCD and AD populations.

Keyphrases: Compensation, Connected speech, Speech acts, Functional speech assessment, Ecological tasks, Mild neurocognitive disorder, Alzheimer's disease, Early detection, Cognitive decline, Activities of daily living