Electrophysiological evidence that unitization is an effective strategy for increasing episodic familiarity

How can the loss of recollection in aging and disease best be alleviated? One avenue of research is to examine the benefits of encoding strategies on memory, including the use of 'unitization', whereby multi-component stimuli are encoded as a single item rather than as a set of associated parts. Recent studies of associative recognition suggest that unitization can improve episodic memory by increasing the availability of familiarity during retrieval, helping to alleviate deficits in recollection. Here we provide neuroimaging evidence for the benefits of unitization in health adults, in the context of learning novel associations between words. We compared memory for word pairs learnt using compound definitions (i.e. VEGETABLE-BIBLE: reference book on gardening) to memory for word pairs learnt using sentence frames (i.e. TOKEN-POUND: The_for the ride cost a_). We employed a standard associative recognition paradigm and measured neural activity during retrieval using Event-Related Potentials (ERPs). Behavioural results indicated that compound definitions (compared to sentence frames) produced a selective memory benefit in terms of both discrimination accuracy and response time. Analysis of ERP data was focused on retrieval-related old/new effects thought to reflect recollection and familiarity. Clear left parietal old/new effects (recollection) were observed regardless of encoding condition. By contrast, mid frontal old/new effects were only observed when stimuli were encoded using the compound definition strategy. The results provide electrophysiological evidence for unitization using compound definitions, demonstrating improved associative recognition via a selective increase in familiarity during retrieval, and validating this method for use in investigations of memory decline.