The influence of semantic prior knowledge on associative memory in healthy aging

peer reviewedLa création d’un souvenir épisodique requiert un encodage des différents éléments composant l’événement cible, ainsi que des associations entre ces éléments individuels afin de former un souvenir global et complexe. Cette capacité à lier les éléments entre eux diminue dans le vieillissement normal engendrant un déclin en mémoire épisodique qualifié « d’associatif ». Des études suggèrent que ce déclin peut être atténué lorsque les associations à mémoriser préexistent en mémoire sémantique. Cette revue a pour but de synthétiser les travaux ayant examiné l’influence des connaissances préexistantes en mémoire associative dans le vieillissement normal. À travers une analyse des procédures utilisées dans les études passées, nous suggérons que le paradigme expérimental employé est le principal facteur qui détermine si les participants âgés peuvent utiliser efficacement leurs connaissances préexistantes pour reconnaître des associations. Plus précisément, la manière dont les paires de stimuli sont recombinées entre l’encodage et la récupération semble avoir une forte influence sur les résultats obtenus. Par ailleurs, nous suggérons un rôle du type de relation sémantique impliquée dans la tâche. La nature de la relation sémantique influencerait en effet la mise en place des processus de reconnaissance épisodiques qui évoluent différemment avec l’avancée en âge.The formation of a global and complex episodic memory requires memory for single units of information of the target event but also binding these elements together. This binding capacity diminishes in healthy aging leading to a so-called associative memory deficit. Interestingly, when support is provided during encoding thanks to semantic prior-knowledge (e.g., semantically related word pairs), this associative deficit can be alleviated. The aim of the present review is to summarize the current literature about the influence of prior-knowledge on associative memory performance in healthy aging. Through an analysis of the procedures that have been used in associative memory studies, we suggest two factors that appear to modulate the impact of prior knowledge on older adults’ associative memory. First, the way word pairs are recombined from the encoding to the retrieval phase is the main factor that has to be taken into account. Conditions that promote recall-to-reject discrimination processes lead to similar performance in older compared to younger adults, whereas conditions that require recollection discrimination lead to an age-related decline. Second, the nature of the semantic relations involved in the prior-knowledge support may influence older adults’ performance by modulating the contribution of recollection and familiarity to recognition. Indeed, categorical semantic relations engage both recollection and familiarity-based discrimination, whereas thematic relations allow participants to rely on familiarity-based discrimination only. This latest observation is crucial when one considers recollection as a declining process, in contrast to familiarity, which remains spared in healthy aging. Therefore, future studies should explore the propensity of other semantic relations to alleviate the age-related associative memory decline

COGNITIVE AND NEUROPSYCHOLOGICAL EXPLORATION OF EPISODIC MEMORY FUNCTIONING: RECOGNITION MEMORY PROCESSES AND MEMORY FOR TEMPORAL CONTEXT

The main objective of our dissertation was to contribute to a better understanding of the cognitive processes involved in episodic memory and their cerebral substrates. More specifically, our work focused on two questions. First, we were interested in the contribution of recollection and familiarity to recognition memory. On the one hand, we examined the performance on recognition tasks when recollection cannot be used anymore (studies 1, 2 and 3) and, on the other hand, the influence of frontal lobe lesions on the processes involved in a recognition memory task (study 4). Second, we explored the processes recruited in an important aspect of episodic memory, namely, memory for the temporal context of events, by studying the nature of the difficulties encountered by older adults on a task assessing memory for temporal information (studies 5 and 6).ARC 99/04-24

Computer Aided Diagnosis System Based on Random Forests for the Prognosis of Alzheimer’s Disease

peer reviewedIn this abstract, we propose an original CAD system consisting in the combination of brain parcelling, ensemble of trees methods, and selection of (groups of) features using the importance scores embedded in tree-based methods. Indeed, on top of their ease of use and accuracy without ad hoc parameter tuning, tree ensemble methods such as random forests (RF) (Breiman, 2001) or extremely randomized trees (ET) (Geurts et al., 2006) provide interpretable results in the form of feature importance scores. We also compare the performance and interpretability of our proposed method to standard RF and ET approaches, without feature selection, and to multiple kernel learning (MKL). The latter was shown to be an efficient method notably capable of dealing with anatomically defined regions of the brain by the use of multiple kernels

Misrecollection prevents older adults from benefitting from semantic relatedness of the memoranda in associative memory.

Memory for episodic associations declines in aging, ostensibly due to decreased recollection abilities. Accordingly, associative unitization - the encoding of associated items as one integrated entity - may potentially attenuate age-related associative deficits by enabling familiarity-based retrieval, which is relatively preserved in aging. To test this hypothesis, we induced bottom-up unitization by manipulating semantic relatedness between memoranda. Twenty-four young and 24 older adults studied pairs of object pictures that were either semantically related or unrelated. Participants subsequently discriminated between intact, recombined and new pairs. We found that semantic relatedness increased the contributions of both familiarity and recollection in young adults, but did not improve older adults' performance. Instead, they showed associative deficits, driven by increased recollection-based false recognition. This may reflect a "misrecollection" phenomenon, in which older adults make more false alarms to recombined pairs with particularly high confidence, due to poorer retrieval monitoring regarding semantically-related associative probes

Cortical and subcortical contributions to state- and strength-based perceptual judgments

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Impaired explicit self-awareness but preserved behavioral regulation in patients with Alzheimer Disease

Objectives: Impairments of metacognitive skills represent a critical symptom in Alzheimer Disease (AD) because it frequently results in a lack of self-awareness. However, recent findings suggest that, despite an inability to explicitly estimate their own cognitive functioning, patients might demonstrate some implicit recognition of difficulties. In this study, we tested whether a behavioral dissociation between explicit and implicit measures of metacognition can be found in both healthy older controls (n = 20) and AD patients (n = 20). Methods: Our two groups of participants (AD vs. Controls) were asked to complete a forced-choice perceptual identification test and to explicitly rate their confidence in each decision (i.e., explicit measure of metacognition). Moreover, they also had the opportunity to ask for a cue to help them decide if their response was correct (i.e., implicit measure of metacognition). Results: Data revealed that all participants asked for a cue more often after an incorrect response than after a correct response in the forced-choice identification test, indicating a good ability to implicitly introspect on the results of their cognitive operations. On the contrary, only healthy participants displayed metacognitive sensitivity when making explicit confidence judgments. Conclusion: Our findings suggest that implicit metacognition may be less affected than explicit metacognition in Alzheimer’s disease

Testing a New Memory Task Sensitive to Early Entorhinal/Perirhinal Atrophy in Alzheimer's disease

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