Grouping mechanisms in response preparation investigated with event-related brain potentials

Preliminary information about responses facilitates performance, especially when the information can be grouped into stimulus-response sets, for example, into fingers belonging to the same hand. Here, we studied the mechanisms of supposedly fast and automatic exogenous as compared to slow and controlled endogenous grouping of same-hand fingers. As compared to endogenous cuing, exogenous cuing facilitated reaction times and induced larger amplitudes of the contingent negative variation, but did not show any advantage in amplitude or latency of the lateralized readiness potential or in the magnitude of current source density over the motor cortices. Similarly, the stimulus preceding negativity did not seem to be a plausible explanation for the observed effect. Therefore, at least one functional mechanism underlying exogenous stimulus-response grouping appears to be the facilitation of central response programming.