To investigate the effects of upper central nervous system on cochlear micromechanics, distortion product otoacoustic emissions (DPOAE) with and without a visual attention task were studied in 16 young subjects with normal hearing. The results showed that the DPOAE (2f1-f2) amplitude were reduced, and significantly decreased in 1 kHz and 2 kHz of F2. In the underlying mechanism of the effects, it is possible that the upper central nervous system facilitate the olivocochlear efferent system and then modulate the cochlear functions. It is suggested that the whole efferent system (from cerebral cortex to olivocochlear bundle) would be of great importance for cochlear function.