Electrophysiological evidence for the effect of interactive imagery on episodic memory: encouraging familiarity for non-unitized stimuli during associative recognition

Episodic memory depends upon multiple processes, including familiarity and recollection. Although associative recognition tasks are traditionally viewed as requiring recollection, recent research suggests a role for familiarity if to-be-remembered stimuli are perceived as unitized. Here we use event-related potentials (ERPs) to examine the relationship between stimulus properties and encoding strategy on the engagement of familiarity during associative recognition. Participants studied word pairs containing an association (e.g. traffic-jam) or an unassociated semantic relationship (e.g. violin-guitar), using either item or interactive imagery. At test, participants were required to recognize if word pairs were presented in the same pairing as study, were rearranged, or new. We hypothesized that adopting a strategy of interactive imagery during encoding (i.e. encouraging unitization) would enhance familiarity for unassociated word pairs but would have no effect on association pairs because they are already perceived as unitized. As expected, overall recognition performance was better for word pairs encoded with interactive imagery, and for association than semantic word pairs. ERPs recorded at test revealed an interaction between encoding strategy and stimulus properties. Association word pairs elicited similar bilateral frontal (familiarity) and left parietal (recollection) old/new effects following item and interactive imagery. By contrast, for semantic word pairs, the left parietal effect was equivalent across conditions, but the bilateral frontal effect was enhanced for the interactive imagery condition. The ERP results suggest that an encoding strategy of interactive imagery can enhance familiarity during associative recognition, but this effect is ultimately dependent on the properties of the stimuli to-be-remembered and the nature of the representations that underlie them.