Background

The base of the basilar membrane is tightly wound and thus more responsive to high frequencies, whereas the apex is loose and responsive to lower frequencies. Indeed, 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 this activity, we again return to the cochlea, but focus on changing the frequency of the tone. For each frequencies observe how the height of the traveling wave changes as it proceeds down the basilar membrane so that there is a point a long the basilar membrane where it responds the most strongly. For each frequency that point is different.

Instructions

Full Screen Mode

To see the illustration in full screen, which is recommended, press the Full Screen button, which appears at the top of the page.

Illustration Tab

Settings

On the Illustration tab, you can adjust these parameters:

Play the Sound: check to start the animation and uncheck to stop the animation.
What Parts of the Ear to Show: Select what part of the ear you wish to examine: the Cochlea, or just the Basilar Membrane.
Frequency (Hz): adjust to see how the cochlea and basilar membrane respond to different frequencies.
Amplitude: make the sound more or less intense.
Show the Envelope: show an outline of the complete motion of the basilar membrane to help show the changes in the height of the traveling wave along the basilar membrane. 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.

Reset

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.

Adjust these parameters to explore how sound stimulates the ear.
Play the Sound
What Parts of Ear to Show: Cochlea Basilar Membrane


Show the Envelope
Show the Frequencies on the Basilar Membrane

Start the sound and observe how the pressure wave moves from the base to the apex. The traveling wave grows and then shrinks suddenly. Change the Frequency of the sound to see how this point of maximal movement changes with different frequencies.