Relation between auditory stimulus intensity and response of P300 with eyes-opened and eyes-closed state

For the purpose of examining how the auditory stimulus level and the eyesight have a mutual influence on ERP, we tried to investigate the relation between auditory stimulus level and latency of P300 with eyes-opened (EO) and eyes-closed (EC) state. Two auditory stimulus levels are selected as high-intensity (HI; 80 dBNHL) and low intensity (LI; 10 dBNHL). It has been regarded that the latency of P300 became longer as the auditory stimulus level decreased while the latency was not so different between EO and EC. However, we found that the latter did not always hold true though the former coincided with our experimental results. The latency at HI tended to be longer comparatively with EO, while in the case of LI the latency was longer with EC. Consequently, the latency variation resulting from the change of stimulus level with EC was larger than with EO. In this paper, we evaluated this phenomenon more quantitatively