Abstract

Event-related potentials were recorded from normal subjects in an auditory selective attention task. The focus of this study was the effect of processing load on event-related potentials(ERPs). Subjects were instructed to selectively attend to tones of designated ear and to respond to those that were higher in frequency by pressing a corresponding response button. Processing load was manipulated by the difficulty level of discrimination between standards and deviants. The standard stimuli were 1000Hz, 60dB SPL, tone burst. The deviant stimuli were only differed in frequency. In the easy task condition, the deviant stimuli were 1500Hz and in the hard task condition, they were 1050Hz. Performance was more accurate and faster in the easy task. These results show that the task condition was reliable. Attention effect(Nd) to standard stimuli peaked at approximately 240msec with a maximal amplitude at Fz. The latency of Nd was dissociated from that of N1. Thus we can conclude that the attention effect was not caused by N1 enhancement but by the activity of processing negativity(PN). The task effect was appeared to the later ERP components. The amplitude of P3b was decreased in the hard task as in previous studies. The result showing the ineffectiveness of attention on N1 suggests that the process to analyze physical features of auditory stimulus can be automatic. The task effect was shown only on the later components of the ERP, therfore we can conclude that the processing load does influence in the later stages of auditory stimulus processing.