The displacement of the basilar membrane in response to frequency is quite specific. Each location along the basilar membrane responds to a characteristic frequency. Any sound will move the basilar membrane at every location, but a particular location will respond the most, in terms of movement, to its characteristic frequency. In the most common case, in which we hear a number of complex sounds, complete with harmonics, the basilar membrane will reflect these frequencies by moving at various places along its length. In effect, the basilar membrane does a Fourier analysis, breaking down complex sounds into their component frequencies (von Békésy, 1960).
In this activity, you can observe the motion of the basilar membrane in the cochlea in response to one or more sounds. You can adjust the frequency and amplitude of each sound separately.
To see the illustration in full screen, which is recommended, press the Full Screen button, which appears at the top of the page.
On the Illustration tab, you can adjust these parameters:
Play the Sound 1: check to play the sound indicated by the sliders below.
Frequency 1 (Hz): adjust the frequency of the this first sound.
Amplitude 1: make the first sound more or less intense.
Play the Sound 2: check to play the sound indicated by the sliders below.
Frequency 2 (Hz): adjust the frequency o the second sound.
Amplitude 2: make the second sound more or less intense.
Show the Frequencies on the Basilar Membrane : check to add numbers below the basilar membrane to indicate the area where different frequencies will have their maximal response.
Pressing this button restores the settings to their default values and allows you to adjust speed and relative size. It also resets the counter before you can indicate if you have the objects arriving at the same time.