Hearing in mammals, depend on an amplifying motion which hypothetically uses force from outer hair cells (OHC) motility to enhance sound induced vibration of the organ of Corti of cochlea. In this hypothesis the differential motion among key structures in this organ and the timing of the OHC force generation is essential for cochlear amplification to occur. Using a time domain optical coherence tomography system which allows us to make vibration measurements we were able to measure differential motion of two functionally important surfaces, namely, basilar membrane and reticular lamina. The reticular lamina vibrates at higher amplitude than the basilar membrane and has significant phase lead over basilar membrane vibration. The differential motion, that is, different amplitude and phase of vibration, become less as the energy of the sound stimulus is increased and the amplification processes in the organ of Corti are quenched.