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 strategic processing related to context updating. Using independent-components analysis (ICA), the present study examined the role of P300 in the tactical process of response selection. Methods: In a task crossing manipulations of perceptual difficulty (PD) and response-selection difficulty (R-SD), ICA was employed to measure not only P300 latency, but its onset and duration as well. Results: Increased PD delayed P300 latency and onset in parallel, while increased R-SD lengthened P300 duration. Conclusions: The latency and onset results suggest that the often-cited covaration of P300 latency with stimulus-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 well-known relation to stimulus probability indicates a strategic role, our findings indicate a tactical role as well.