Convertino, Laura; (2024) Navigating Spatial, Temporal, and Semantic Contexts in Memory. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Context is fundamental to create a coherent understanding of experience, index memories and control generalisation from them. Although context has been defined in a variety of ways, clear understanding of how different contextual cues interact and interfere with each other is still missing. Here, I investigate possible behavioural, computational, and neuronal mechanisms of temporal, semantic and spatial context. In Chapter 2, I first implemented a modified version of the Deese-Roediger-McDermott (DRM) paradigm for false memory. This allowed me to investigate the interaction and interference of semantic and temporal context in recognition and source memory. Moreover, an auto-associative (Hopfield) network reproduced the behavioural results and helped me investigate the role of semantic context and pattern completion. I then implemented a successor representation temporal context model, to test how the temporal context interacts with semantic context in free recall. Finally, I developed two generative models of false memory within the active inference framework as Bayesian optimal behaviour. Using magnetoencephalography (MEG), I investigated whether neural populations involved in representing spatial context (grid cells) could be impaired in patients with schizophrenia [Chapter 3]. We were able to find 6-fold modulated theta activity in the entorhinal cortex during virtual navigation in healthy controls, but not in schizophrenic patients. This suggests that impairments in knowledge structuring and relational inference associated with schizophrenia may arise from disrupted grid firing patterns. Finally [Chapter 4], I developed an fMRI task to investigate whether retrieving a list of words corresponds to navigation of a 2-dimensional abstract space, whose axes are organised over the temporal and semantic distance between words, and whether a grid-like code is used for this. In summary, my work suggests that semantic and episodic memory are deeply interconnected, and that different forms of context - spatial, temporal and semantic - interact and interfere in memory retrieval.

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