In what way does the parietal ERP old/new effect index recollection?

Event-related potentials (ERPs) were recorded while subjects performed a memory retrieval task requiring old/new judgements to visually presented old (previously studied) and new words. For words judged old, subjects made two binary forced-choice context (hereafter source) judgements, denoting the voice (male/female) and task (action/liking) with which the test word had been associated at study. By separating the ERPs according to the accuracy of the voice and task judgements, it was possible to test the prediction that the differences between ERPs to correctly identified old and new words at parietal scalp sites (parietal old/new effects) are sensitive to the amount or quality of information that is retrieved from episodic memory (Rugg, M.D., Cox, C.J.C., Doyle, M.C., Wells, T., 1995. Event-related potentials and the recollection of low and high frequency words. Neuropsychologia 33, 471–484). In keeping with this proposal, the magnitude of the parietal old/new effects co-varied with the number of accurate source judgements. This finding is consistent with proposals that the parietal old/new effect indexes recollection in a graded fashion