P3 (viz. P300) is a most prominent component of event-related EEG potentials recorded during task performance. There has been long-standing debate about whether the process reflected by P3 is tactical or strategic, i.e., required for making the present response or constituting some overarching process. Here, we used residue iteration decomposition (RIDE) to delineate P3 subcomponents time-locked to responses and tested for the temporal relations between P3 components and response times (RTs). Data were obtained in oddball tasks (i.e., tasks presenting two stimuli, one rarely and one frequently) with rare and frequent go, no-go, or choice responses (CRs). As usual, rare-go P3s were large at Pz and rare no-go P3s at FCz. Notably, P3s evoked with rare CRs were large at either site, probably comprising both go and no-go P3. Throughout, with frequent and rare responses, P3 latencies coincided with RTs. RIDE decomposed P3 complexes into a large CPz-focused C-P3 and an earlier Pz-focused response-locked R-P3. R-P3 had an additional large fronto-central focus with rare CRs, modeling the no-go-P3 part, suggesting that the process reflected by no-go P3 is tightly time-locked to making the alternative response. R-P3 coincided with the fast RTs to frequent stimuli and C-P3 coincided with the slower RTs to rare stimuli. Thus, the process reflected by C-P3 might be required for responding to rare events, but not to frequent ones. We argue that these results are nevertheless compatible with a tactical role of P3 because responses may not be contingent on stimulus analysis with frequent stimuli.
Keywords: Context updating; Decision; P300; RIDE.
Copyright © 2016 Elsevier Inc. All rights reserved.