In this study, we measured the point of subjective simultaneity (PSS) between auditory and visual stimuli under various conditions of illuminance at the subject's eyes. The test stimuli were a pure tone of 1000 Hz at a sound pressure level of 50 dB and a white light (LED). Both sound and light stimuli had a duration of 10 ms. The luminance of the LED was set at 21.2 cd/m~2, and the ambient illuminance around the LED was set at 0 1x. The illuminance at the subject's eyes was adjusted to 0, 500, or 1000 lx using a spotlight located above the subject's head. The test stimuli had a stimulus onset asynchrony (SOA) of 0, ±20, ±40, ±80, or ±160 ms, where positive values indicate that the visual stimulus was presented first. Four men in their early 20s participated in the experiments. We presented the test stimuli to the subject with the nine SOAs in random order. After each presentation of the test stimuli, we asked subjects to answer which of the stimuli - sound or light - they perceived first. Then we evaluated the PSS of the test stimuli and considered the influence of illuminance at the eyes on the PSS. As a result, the PSS shifted toward positive direction, i.e., the perception of light precedence as the illuminance at the eyes increased.
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