Sequence effects in the Go/NoGo task: inhibition and facilitation.

Facilitation and inhibition are asymmetric aspects of attention that differentially affect response times (RTs), accuracy and neuroelectric activity in many experimental tasks. Both vary as a function of stimulus context, with stimulus repetitions, for example, often resulting in facilitation in terms of speed, accuracy or reduced neural activity. Although inhibition has been extensively studied in the Go/NoGo task, facilitation has been overlooked. Twenty healthy adults performed an adapted Go/NoGo task which manipulated levels of facilitation and inhibition. Event-related potential (ERP) and behavioural measures were averaged according to preceding stimulus sequences. Established Go/NoGo effects for N2 and P3 components were replicated. Behavioural and ERP measures, however, showed strong sequence effects. Correlates of facilitation included reduced P1 and N1 latencies, and topographic effects in P1, to Go stimulus repetitions. Manipulations of inhibitory load through increasing Go before NoGo stimuli resulted in incremental increases in N1, P2 and N2 latencies. Several additional ERP and RT measures showed quadratic effects, with indications of facilitation or inhibition which reversed towards the end of longer stimulus trains. The results suggest that both facilitatory and inhibitory processes underlie performance in the Go/NoGo task. As Go stimuli are typically more frequently repeated than NoGo stimuli, the two processes may be confounded when sequence effects are not considered. Additionally, analysing stimuli by context indicates that the timing of the Go-P3 latency is closely related to responses, and the prolongation of N1, P2 and N2 with increasing difficulty of inhibition supports a possible relation of these components to inhibition.