The impact of change in stimulus format on the electrophysiological indices of recognition.

The present study investigated the impact of changes in stimulus format between study and test on the event-related potential (ERP) correlates of recognition. To this end subjects studied the names and pictures of common objects. At retrieval, subjects were presented with old items for which the presentational format had changed (from picture to name or vice versa), old items that were shown in the same format as at study, and new items. ERPs revealed three temporally, spatially and functionally dissociable memory-related effects: an early bilateral frontal effect, which was sensitive to the perceptual similarity between study and test stimulus; a left temporo-parietal effect, which was sensitive to the type of stimulus that was encoded; and a late frontal effect, which was largest over right electrode sites and appeared to be sensitive to the type of test stimulus. The results provide further evidence for a functional dissociation between the early bilateral frontal and the later temporo-parietal old/new effect, suggesting an interpretation in terms of processes contributing to a perceptually-driven familiarity or novelty assessment and recollection, respectively.