Accessory stimulus effects on response selection: Does arousal speed decision making?

When an intense but task-irrelevant "accessory" stimulus accompanies the im perative stimulus in a choice reaction task, reaction times (RTs) are facil itated. In a similar previous study (Hackley & Valle-Inclan, 1998), we show ed that this effect is not due to a reduction of the interval from onset of the lateralized readiness potential (LRP) until movement onset. In the pre sent study, the RT task was modified to move a portion of the response sele ction stage into this time interval. The interval remained invariant, indic ating that this late phase of the response selection process is not speeded by accessory stimulation. However, we observed amplitude modulation of the LRP on no-go trials in a condition with three alternative responses. This finding suggests that an earlier phase of response selection is influenced by accessory stimulation. In addition, a novel dependent measure was introd uced to event-related potential research-the latency of spontaneous, posttr ial blinking.