Cognitive and neural basis of memory for associations and order

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Memory for associations (pairs, such as Notley-Alberta or William-Kate) and memory for order (sequences, such as a phone number) are critical for complex behaviour, from navigation to language to social behaviour. Theories are systematically organized through mathematical models, but these models have also been developed and tested separately for association and order memory. Our aim is to develop a single model that can explain memory behaviour in both standard association and order tasks, but also tasks that combine elements of both. In our approach, with careful design, experiments measuring memory behaviour (accuracy and response time) and brain-activity related to successful encoding can provide powerful tests of models, leading to a deeper and more generalizable unified model of relational memory.Our recent findings show that models must be redesigned. We were the first to ask, when people remember a pair of words, do they remember the association with or without order (was it Christy-Clark or Clark-Christy)? Participants could judge order, even when they did not deliberately study for order. However, order can also be ambiguous, even when the pair of items is remembered. This challenges current models of association: the matrix model (related to Hebb's rule), which learns associations with unambiguous order and convolution-based models, which store associations without order. Second, early models assumed memory of a list (ABCD...) is composed of a "chain" of associations (AB, BC, CD, ...). Pitted against these, "positional-coding" models, which deliberately omit inter-item associations, are now favoured. Our recent findings clearly show that one recall does, in fact, influence the next, overturning a major tenet of positional-coding models and suggesting that associative chaining is a major part of serial-order memory. The next generation of models will need both item-item and item-position associations. Third, we challenged previous arguments that some brain-activity signals in item-memory tasks reflected associative processes. Instead, frontal slow waves and theta rhythms (4-8 cycles/second) rhythms may be specifically critical for association, and perhaps order, memory.We will modify current models of association- and order-memory to accommodate these findings and generate new testable predictions. In parallel, we will conduct behavioural and electroencephalographic experiments to better understand the relationship between memory for associations and memory for order, and to test and guide further model development.Combining mathematical models, behavioural and brain-activity methods, we can better understand memory behaviour at a basic level, potentially identify brain-activity signals that could be targets of memory assessment or enhancement protocols, and guide the development of memories in artificial agents.