There is more to memory than recollection and familiarity.

Theoretical models of memory retrieval have focused on processes of recollection and familiarity. Research suggests that there are still other processes involved in memory reconstruction, leading to experiences of knowing and inferring the past. Understanding these experiences, and the cognitive processes that give rise to them, seems likely to further expand our understanding of the neural substrates of memory

Towards Lifelong Reasoning with Sparse and Compressive Memory Systems

Humans have a remarkable ability to remember information over long time horizons. When reading a book, we build up a compressed representation of the past narrative, such as the characters and events that have built up the story so far. We can do this even if they are separated by thousands of words from the current text, or long stretches of time between readings. During our life, we build up and retain memories that tell us where we live, what we have experienced, and who we are. Adding memory to artificial neural networks has been transformative in machine learning, allowing models to extract structure from temporal data, and more accurately model the future. However the capacity for long-range reasoning in current memory-augmented neural networks is considerably limited, in comparison to humans, despite the access to powerful modern computers. This thesis explores two prominent approaches towards scaling artificial memories to lifelong capacity: sparse access and compressive memory structures. With sparse access, the inspection, retrieval, and updating of only a very small subset of pertinent memory is considered. It is found that sparse memory access is beneficial for learning, allowing for improved data-efficiency and improved generalisation. From a computational perspective - sparsity allows scaling to memories with millions of entities on a simple CPU-based machine. It is shown that memory systems that compress the past to a smaller set of representations reduce redundancy and can speed up the learning of rare classes and improve upon classical data-structures in database systems. Compressive memory architectures are also devised for sequence prediction tasks and are observed to significantly increase the state-of-the-art in modelling natural language

The hippocampus reevaluated in unconscious learning and memory: at a tipping point?

Classic findings from the neuropsychological literature invariably indicated that performances on tests of memory that can be accomplished without conscious awareness were largely spared in amnesia, while those that required conscious retrieval (e.g., via recognition or recall) of information learned in the very same sessions was devastatingly impaired. Based on reports of such dissociations, it was proposed that one of the fundamental distinctions between memory systems is whether or not they support conscious access to remembered content. Only recently have we come to realize that the putative systemic division of labor between conscious and unconscious memory is not so clean. A primary goal of this review is to examine recent evidence that has been advanced against the view that the hippocampus is selectively critical for conscious memory. Along the way, consideration is given to criticisms that have been levied against these findings, potential explanations for differences in the reported results are proposed, and methodological pitfalls in investigations of unconscious memory are discussed. Ultimately, it is concluded that a tipping point has been reached, and that while conscious recollection depends critically on hippocampal integrity, the reach of the hippocampus extends to unconscious aspects of memory performance when relational memory processing and representation are required

Disturbing visual working memory:electrophysiological evidence for a role of the prefrontal cortex in recovery from interference

Single cell recordings in monkeys support the notion that the lateral prefrontal cortex (PFC) controls reactivation of visual working memory representations when rehearsal is disrupted. In contrast, recent fMRI findings yielded a double dissociation for PFC and the medial temporal lobe (MTL) in a letter working memory task. PFC was engaged in interference protection during reactivation while MTL was prominently involved in the retrieval of the letter representations. We present event-related potential data (ERP) that support PFC involvement in the top-down control of reactivation during a visual working memory task with endogenously triggered recovery after visual interference. A differentiating view is proposed for the role of PFC in working memory with respect to endogenous/exogenous control and to stimulus type. General implications for binding and retention mechanisms are discussed

Ageing and episodic retrieval: using event-related potentials to compare the neural correlates of item and associative recognition in young and older adults.

Older people commonly report problems with remembering, and behavioural studies have confirmed that memory does decline with age. Age-related deficits are particularly evident in episodic memory; however, the degree of impairment appears to be task-dependent. Compared to young adults, older adults generally perform reasonably well on simple item recognition tasks, but are markedly compromised on more complex tasks, such a s those that require memory for context. Dual process theory suggests that this pattern of ageing deficits results from an age-related decline in recollection, whilst familiarly remains relatively intact. This thesis reports a series of event-related potential (ERP) studies conducted to examine the effect of ageing on the neural correlates of simple item recognition and more complex associative recognition. Behaviourally, as anticipated, the young outperformed the elderly, particularly in associative recognition. Electrophysiologically, the age-related reduction of the left parietal effect in item recognition appeared to support the dual process view that recollection becomes compromised as people grow older. Likewise, an early right frontal component, evident in both item and associative recognition, may reflect the preservation of familiarity in elderly adults. However, the ERP data also suggest that dual process theory may represent an oversimplification of episodic memory age decline. While the presence of a left parietal sam e/rearranged difference in young adults was interpreted as evidence of the adoption of a target-specific recollection strategy in associative recognition, the modulation's absence in older adults suggests that they are unable to similarly inhibit the retrieval of goal-irrelevant information. Moreover, the older participants also demonstrated widespread left-sided negative activations that may represent two components: First, the fronto-central negativities elicited by both tasks may index the compensatory operations recruited by older adults to maximise their performance. Second, a central/posterior negativity in item recognition, which strongly resembled a modulation that had been previously observed in source memory ageing studies, was interpreted as reflecting the task-irrelevant retrieval of contextual information