P300 and response selection: A new look using independent-components analysis

Purpose: The most prevalent current view of the functional role of the P300 component of the event-related potential (ERP) is that it indexes strategi c processing related to context updating. Using independent-components anal ysis (ICA), the present study examined the role of P300 in the tactical pro cess of response selection. Methods: Ln a task crossing manipulations of pe rceptual difficulty (PD) and response-selection difficulty (R-SD), ICA was employed to measure not only P300 latency, but its onset and duration as we ll. Results: Increased PD delayed P300 latency and onset in parallel, while increased R-SD lengthened P300 duration. Conclusions: The latency and onse t results suggest that the often-cited covaration of P300 latency with stim ulus-evaluation time is secondary to effects on processing stages preceding P300. The results for duration indicate that P300 is involved in response selection, suggesting that it is not a unitary phenomenon. While P300's wel l-known relation to stimulus probability indicates a strategic role, our fi ndings indicate a tactical role as well.