Effects of degradation of visual stimulation on components of the event-related potential (ERP) in go/nogo reaction tasks.

In the present experiments, event-related potentials (ERPs) were measured to randomly presented letters, requiring either a right-hand button-press response (go), or requiring no response (nogo). In both go and nogo conditions, the letters could be intact or degraded. ERPs time-locked with voluntary right hand button-presses were measured in a separate condition. Nogo stimuli elicited larger negative components (N400, N480) at the frontal electrode sites, and larger late-positive components (P600, P640) at the central electrode sites, than go stimuli. Additionally, intact stimuli elicited larger late-positive components and smaller Slow Wave (SW) components then degraded stimuli, but these amplitude-differences were seen more clearly in the nogo than in the go conditions. These results are discussed in relation to cognitive and motor aspects of go and nogo stimuli, and the possibility of contamination of ERP components with movement-related potentials.