Effect of seat vibration on sleepiness of the driver exposed to interior noise of small diesel truck — Trial for a model representing sleepiness using physiological data as predictor variables : Takeo Hashimoto, Shigeko Hatano (Seikei University), Ayumi Kasai (NSK Ltd.), Yoshihiro Noguchi (Isuzu Advanced Engineering Center Ltd.), Haruki Saito (Isuzu Motors Ltd.)