Gerbil middle-ear sound transmission from 100 Hz to 60 kHz

Middle-ear sound transmission was evaluated as the middle-ear transfer admittance H M Y (the ratio of stapes velocity to ear-canal sound pressure near the umbo) in gerbils during closed-field sound stimulation at frequencies from 0.1 to 60 kHz , a range that spans the gerbil's audiometric range. Similar measurements were performed in two laboratories. The H M Y magnitude (a) increased with frequency below 1 kHz , (b) remained approximately constant with frequency from 5 to 35 kHz , and (c) decreased substantially from 35 to 50 kHz . The H M Y phase increased linearly with frequency from 5 to 35 kHz , consistent with a 20 - 29 μ s delay, and flattened at higher frequencies. Measurements from different directions showed that stapes motion is predominantly pistonlike except in a narrow frequency band around 10 kHz . Cochlear input impedance was estimated from H M Y and previously-measured cochlear sound pressure. Results do not support the idea that the middle ear is a lossless matched transmission line. Results support the ideas that (1) middle-ear transmission is consistent with a mechanical transmission line or multiresonant network between 5 and 35 kHz and decreases at higher frequencies, (2) stapes motion is pistonlike over most of the gerbil auditory range, and (3) middle-ear transmission properties are a determinant of the audiogram.