Readiness to retrieve memories of different ages: An ERP dissociation of orienting and difficulty

A well-established finding in episodic memory research is that the likelihood of successful retrieval is affected by the age of the targeted memory (i.e. based on the duration of the encoding-retrieval interval). Although such findings are usually interpreted in terms of the memory trace changing in quality or accessibility over time, there is growing evidence that memory performance also depends on preparatory attention and strategic orienting at the time of retrieval. Here, we investigated such readiness to retrieve, as indexed by event-related brain potentials (ERPs), when memory retrieval was aimed toward candidate traces of different ages. As retrieving remote versus recent memories is associated with increased difficulty, the current study was designed to dissociate difficulty from the memory age effects. Subjects encoded two lists of pictures separated by one week, with the items in each list presented once or four times. A series of memory tests targeting pictures from only one week-by-repetition condition at a time were then completed, while new pictures and those from the other conditions were rejected. Consistent with previous results, new-item ERPs were more positive over posterior scalp when recent compared to remote lists were targeted. Importantly, this difference remained when difficulty was matched, and the ERP correlates of difficulty were distinct in both timing and polarity from those of orienting. Together, these findings provide further support for the idea that the age of a targeted memory alone places different demands on readiness and can lead to the differential adoption of retrieval orienting strategies.