Decomposition of the ERP late posterior negativity: effects of retrieval and response fluency

Negativity elicited by recognized items over posterior sites--the late posterior negativity (LPN)--has been linked to action monitoring, task "uncertainty," and contextual retrieval. Four recognition tests required retrieval of encoding operations. Task fluency was assumed to increase with each block. The responses assigned to the episodic sources were reversed in Block 3 to reduce response fluency. Dissociable LPNs were identified; the 1200-1900-ms LPN was insensitive to task and response fluency and may reflect the maintenance of a retrieved episode. The 600-1200-ms LPN was sensitive to task fluency and may index the search for episodic information. A response-related LPN was sensitive to response fluency and was consistent with an action monitoring role. The findings confirm that the LPN is functionally heterogeneous, and comprises subcomponents sensitive to retrieval fluency, action monitoring, and postretrieval processing respectively.