1. Mechanical stimulation of the tympanic membrane with vibrating probes eliminates the acoustic tuning of the receptor and allows the mechanical tuning to be determined.

2. Using neural firing rates as a measure of the response magnitude, three separate regions of high sensitivity are found. They are centred at approximately 2, 14 and 60 kHz. Displacements of 0.1 to 1.0 Å suffice for excitation at 60 kHz.

3. The regions of high sensitivity appear to correspond to the first, third and fifth order mechanical resonances of the scoloparium.

4. Comparison with the results of acoustic stimulation experiments indicates that low-frequency acoustic stimuli are filtered out by the acoustic system of the receptor.

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