Frequency Analysis by the Ear
Incoming sounds are decomposed into their frequency components at the basilar membrane. The near ("basal") end of the basilar membrane resonates to high frequencies, and the far ("apical") end resonates to low frequencies. Vibrations at different locations on the basilar membrane therefore reveal what frequencies are present in the sound. This little video shows you how the vibrations might look if the basilar membrane could be "rolled out in front of you".
The vibration patterns of the cochlea may remind you of the spectrogram
which you may have played with earlier in this guide.