EFFECTS OF LIGHT STIMULUS UPON SIMPLE REACTION-TIME AND EP LATENCY TO THE CLICK PRESENTED WITH DIFFERENT SOA

Click and light were presented in pairs with varying stimulus onset asynchronies (SOAs) and the subjects were asked to respond to the click onset. SRTs and EPs were obtained for two levels of click intensity and were plotted as a function of SOAs. As the related EP component, Nc, or the negative peak immediately following the click onset, was taken and the Nc recorded from Cz was analyzed. Although the larger Nc amplitudes occurred with shorter SRTs, no systematic changes in Nc amplitude were observed as a function of SOAs. Nc latencies, the variations of which were smaller for an intense click than for a faint one, were shorter for trials in which light preceded click (SOA .ltoreq. 0) than for click-alone trials, in correlation with SRTs. This fact suggests that the light given prior to click increased the arousal level and/or the processing speed. Dimodal facilitating effect of the internal processing speed upon SRTs was obtained at 50 ms of SOA.