Effects of task complexity on ERP components in Go/Nogo tasks

In Go/Nogo tasks the ERP at frontocentral electrodes generally exhibit a negativity (Nogo-N2) and a subsequent positivity (Nogo-P3) after Nogo in contrast to Go stimuli. The N2 was related to central inhibition or response conflict, while the P3 is most probably related to inhibition of overt response. In an attempt to elucidate the underlying processes in more detail, the effects of task difficulty on Nogo-N2 and Nogo-P3 were investigated and compared with effects on components in the Go-ERPs and with behavior. RT and false alarms were enhanced and the Nogo-N2 and the Nogo-P3 delayed with rising task difficulty. However, the latency effects were smaller for the Nogo-N2 than for the Nogo-P3. The amplitude of the Nogo-P3 decreased with rising task difficulty but no effects on the Nogo-N2 amplitude were found. In the Go trials an early frontocentral positivity (Go-P2) and a late parietal positivity (Go-P3) were seen. The Go-P2 and Go-P3 showed again similar latency effects as RT, while the amplitudes were not affected by task difficulty. The Go-P3 peaked earlier than the Nogo-P3. The results show that Nogo-N2 and -P3 are differentially affected by the task manipulations. In particular, the Nogo-N2 reflects the inhibition of a premature response plan, which is delayed in more complex tasks, while the Nogo-P3 appears to be linked to inhibition of motor response. The Go-P2 probably reflects stimulus-response activation, which considerably influences the Nogo N2 when measured by the Nogo minus Go difference waves (N2d), whereas the Nogo-P3d solely consists of the Nogo-P3.