Otoreflectance of the cochlea and middle ear

Otoreflectance refers to acoustic pressure reflectance measurements in the ear canal, by the use of a leak-free insertion of a probe assembly, in the frequency or time domain over a range of two or more stimulus levels. Otoreflectance includes an iso-level response indicative of the forward transfer of acoustic energy into the middle ear, and nonlinear responses indicative of the acoustic energy reflected back from the cochlea. The nonlinear otoreflectance decouples the reflected energy in an evoked otoacoustic emission (OAE) from its subsequent re-reflected energy due to the presence of the ear-canal probe. Nonlinear otoreflectance responses are extremely sensitive to probe distortion, and a double-evoked (2E) technique, previously used in evoked (OAE) measurements, is adapted for otoreflectance to solve the distortion problem. Results are obtained using a 2E stimulus set containing a set of three click stimuli delivered through a pair of sources. The corresponding sets of three pressure responses are acquired in a calibration tube, and in the ear canal, and a set of three iso-level ear-canal reflectances is calculated. An evoked OAE can be decomposed into a otoacoustic reflected pressure (ORP), and a nonlinear otoreflectance is defined by the ratio of the ORP to the initial pressure spectrum. Otoreflectance provides simultaneous measurements of middle-ear and cochlear responses, and has potential, as yet untested, for application to clinical tests for hearing impairments.