Confidence and accuracy of source memory judgements: which of them modulates prefrontal ERPs?

The aim of the present study was to investigate the role of the prefrontal regions during source memory judgements. In particular, we were interested in disentangling theoretical accounts of the prefrontal involvement based on objective features of the retrieval judgement (retrieval accuracy) and accounts concerning subjective aspects of retrieval (confidence of the decision). Event-related potentials (ERPs) were recorded during the test phase of a memory task in which words were visually presented. The information to be retrieved was the voice of the speaker at study (male vs. female). Additionally, confidence ratings about the source judgement were required. The results show that ERP amplitude was not modulated by the success of the voice retrieval. Conversely, a clear-cut dissociation was observed among the sets of prefrontal electrodes analyzed, along the anterior-lateral and left-right topographical dimensions, respectively. Waves evoked by low-confidence responses were more positive than those evoked by high-confidence ones. This pattern occurred in a set of bilateral anterior frontal sites (1000-2000 ms post-stimulus onset). Moreover, the ERPs were clearly more positive in the right frontal regions than elsewhere (1000-1500 ms post-stimulus), independently of accuracy and confidence. These results suggest a fractionation of functions within the underlying prefrontal areas during this particular memory task, embedding source memory judgements with confidence ratings. In particular, these findings are in conflict with accounts which relate the prefrontal involvement in source memory to the successful retrieval of the source, while support monitoring (anterior frontal effect) and metamemory interpretations (right frontal effect).