Effects of the acoustic reflex on middle-ear transmission and eardrum admittance in man

Abstract

Psychophysical measurements of middle-ear transmission change, 0.4 to 4 kHz, and physical measurements of eardrum acoustic admittance, 0.063 to 4 kHz, have been made on four normal-hearing subjects during activation of the acoustic reflex via contralateral noise, LN′, 80–110 dB SPL. The psychophysical data have been obtained by exploiting the sensitivity of the phase of the aural combination tone 2f1−f2 to primary tone level [W. M. Rabinowitz and J. L. Goldstein, J. Acoust. Soc. Am. 54, 293(A) (1973)]. The admittance measurements have been obtained with a specially designed electroacoustic probe tip assembly coupled to an automated transfer function analyzer. The middle-ear transmission, |H(f)|, changes monotonically with LN. For the maximal elicitor used, LN-max, the average Δ|H(f)| is −10 dB (σ = 1.8 dB) for f ⩽ 0.63 kHz, −2 dB at f = 1.25 kHz, and zero (±1 dB) for f ⩾ 2 kHz. The observed admittance change, Δ|Yd (f)|, for LN-max is −2.5 dB (σ = 1.4 dB) for f ⩽ 0.63 kHz, zero at 1 kHz, +1.5 dB at 1.25 kHz, and zero at 4 kHz. Together the Δ|H(f)| and Yd(f) data provide constraints on possible middle-ear models. [Work supported by NIH.]