Dissociating the influence of affective word content and cognitive processing demands on the late positive potential.

The late positive potential (LPP) elicited by affective stimuli in the event-related brain potential (ERP) is often assumed to be a member of the P3 family. The present study addresses the relationship of the LPP to the classic P3b in a published data set, using a non-parametric permutation test for topographical comparisons, and residue iteration decomposition to assess the temporal features of the LPP and the P3b by decomposing the ERP into several component clusters according to their latency variability. The experiment orthogonally manipulated arousal and valence of words, which were either read or judged for lexicality. High-arousing and positive valenced words induced a larger LPP than low-arousing and negative valenced words, respectively, and the LDT elicited a larger P3b than reading. The experimental manipulation of arousal, valence, and task yielded main effects without any interactions on ERP amplitude in the LPP/P3b time range. The arousal and valence effects partially differed from the task effect in scalp topography; in addition, whereas the late positive component elicited by affective stimuli, defined as LPP, was stimulus-locked, the late positive component elicited by task demand, defined as P3b, was mainly latency-variable. Therefore LPP and P3b manifest different subcomponents.