Measurement of the Amplitude and Phase of Vibration of the Basilar Membrane Using the Mössbauer Effect

Abstract

The Mössbauer effect has been applied to the measurement of the amplitude and phase of the motion of the basilar membrane of the squirrel monkey's cochlea (in vivo). Measurements were taken every 200–300 Hz from 200 to 12 000 Hz in the 6- to 9-kHz region of the cochlea. Measurements of the umbo or incus motion were also taken. Umbo motion was measured at 100–110 dB SPL and was linear over the range of SPLs used. Results of the basilar membrane measurements indicate that the low-frequency portion of basilar membrane-incus transfer characteristic increases at 5–10 dB/oct, while the high-frequency region drops off at a slope of 90–150 dB/oct. The phase difference between the basilar membrane and incus is a linear function of frequency except at low frequencies, where the basilar membrane leads the incus vibration by 90°. The velocity of the traveling wave over this region of the cochlea is 15–20 m/sec. The basilar-membrane measurements were taken at 80–120 dB SPL. The peak excursions of the membrane were on the order of 0.05–0.1 at 5 kHz for 90 dB SPL.