Late ERP components in visual and auditory Go/Nogo tasks.

In an audio-visual Go/Nogo paradigm we studied whether the Go/Nogo difference, usually found in the time range of the visual N2, is also present after auditory stimuli, which bears on the common response inhibition hypothesis of this N2 effect. Moreover the possible presence and variation of P300 subcomponents were studied with the goal of clarifying the reasons for the commonly observed P300 topography changes between Go and Nogo trials. To disentangle possible P300 subcomponents we applied a crossmodal divided attention (DA) condition, in which the subcomponents are known to be separated after auditory stimuli in choice tasks. An N2 effect was found after visual but not after auditory stimuli, which is evidence against the response-inhibition hypothesis. After visual stimuli a positive complex (P400) was seen, whereas after auditory stimuli two dissociated components (P400 and P507) were found instead. The P507 had a parietal maximum for both Go and Nogo trials. It was larger and it peaked later in Go than in Nogo trials. The P400 showed topographic differences between Go and Nogo trials, which could be explained by the overlap of the two subcomponents. We assume that (i) both subcomponents have a stable topography across response type, and (ii) the first subcomponent is invariant with response type, whereas the second (which overlaps the first one) is larger and peaks later on Go than on Nogo trials.