A Parietal Memory Strength Signal Linked to Evidence Accumulation in Recognition Decisions

Recognising objects from memory requires an integration of sensory and mnemonic information. This process has been theorised to occur via a stochastic evidence accumulation process implemented within the parietal cortex. Here, we provide evidence for this type of mnemonic accumulator using a combination of electroencephalographic (EEG) recordings and generative computational modelling. We recorded EEG from participants making recognition judgements based on either studied or novel words. We first demonstrate that the widely studied parietal Late Positive event-related potential Component (LPC) reflects a dynamic decision-making variable occurring prior to the recognition judgments. By fitting Diffusion Decision Models to neural and behavioural data using specialised neural network tools, we then show that the LPC amplitudes are selectively associated with the rate of evidence accumulation, signifying memory strength. This association was stronger for previously studied words compared to novel words. Our findings therefore recast the LPC as a neural signature of mnemonic strength in evidence accumulation for recognition memory judgments, especially for memorised objects.