The FN400 is functionally distinct from the N400.

The FN400 refers to the early midfrontally-distributed difference between ERPs elicited by old and new items, which operates in a way consistent with a neural marker of familiarity-based recognition. Double dissociations between the FN400 and a later ERP index of recollection provide some of the most compelling evidence in support of dual-process models to date. It has recently been claimed, however, that there is no evidence that the FN400 is functionally distinct from the N400 index of implicit semantic priming (Voss, J., and Federmeier, K., FN400 potentials are functionally identical to N400 potentials and reflect semantic processing during recognition testing, Psychophysiology, 48, 532-546, 2011), challenging inferences made on the basis of this effect. We argue that the design employed to make this claim is flawed because it comprised a semantic priming manipulation embedded within a continuous recognition test which enabled recognition contrasts to be confounded by semantic processes in a number of ways. Here, ERPs were recorded from a design which avoided these confounds by employing a semantic priming paradigm which also served as the encoding phase for a surprise subsequent recognition test phase. An N400 effect elicited in the semantic priming task demonstrated the established centro-parietal maximum, whereas the difference between correctly responded to old and new ERPs in the recognition test was maximal over frontal sites in the same time window. When direct comparisons of the electrophysiological correlates of semantic priming and episodic recognition are recorded in a paradigm in which the two are not confounded, the FN400 reflects a qualitatively distinct effect from the N400.