Experimental confirmation of the two-source interference model for the fine structure of distortion product otoacoustic emissions

Abstract

High-resolution measurements of distortion product otoacoustic emissions (DPOAEs) from three different experimental paradigms are shown to be in agreement with the implications of a realistic "two-source" cochlear model of DPOAE fine structure. The measurements of DPOAE amplitude and phase imply an interference phenomenon involving one source in the region of strong nonlinear interaction of the primary waves (the strong "overlap" or generation region), and the other source region around the DPOAE tonotopic place. The component from the DPOAE place can be larger than the one from the generator region. These findings are supported by the analysis of the onset and offset of the DPOAE when the higher-frequency primary is pulsed on and off. The two-source hypothesis was further tested by adding a third tone closer in frequency to the DPOAE which modifies the amplitude of the component from the DPOAE place and leaves the one from the generator region unchanged. The results agree well with the model prediction that the variation with frequency, and implied latency, of the phase of the DPOAE tonotopic-place component are greater than the corresponding quantities for the component from the generation region.

Physiology, Psychoacoustics and Cognition in Normal and Impaired Hearing

“…Each measurement was multiplied by a half-second-long sliding window with a step size of 25 ms, which gives successive windowed signal segments x m n where 1, 2,...,32 n = and m are the indices of repeated number and segments respectively. An artifact-reduced segment x m was obtained by taking a temporal average of the 32 segments having power falling within 75 % of the median, then the magnitude coefficients X m (at frequency (0.025/2) 500 2 m m F = ⋅ ) were evaluated by LSF procedure to the delayed probe stimulus (Long and Talmadge 1997;Talmadge et al 1999;Naghibolhosseini et al 2014). Real-time data processing was controlled by a Fireface UC, using Matlab and Psychtoolbox (Kleiner et al 2007) in a Windows OS programing environment.…”

Modification of DPOAE Fine Structure Stemming from Changes in Outer and Middle Ear Function

“…The energy generated as the 2 f 1 − f 2 distortion product, travels both basally to the oval window (generator component), and apically to the characteristic place corresponding to the DP frequency where some of it is reflected back to the oval window [6]. The pattern of vibration at the oval window, which is the vector sum of the two components, produces vibrations in the middle ear and the ear canal.…”

“…Because the mechanisms of generation are different for the two components described, the slope of phase with frequency is very different for the two components (shallow for the component generated in the overlap region, and steep for the component arising from the DP place). The vector sum of the two components alternates between in and out of phase, resulting in DPOAE fine structure [5,6]. Since DPOAEs are generated in the cochlea, but measured in the ear canal, they depend on the impedance of the middle and outer ear.…”

The short-wave model and waves in two directions

“…These explorations were inspired by the somewhat puzzling properties of otoacoustic emissions from the cochlea, in particular, distortion-product emissions. Two general classes of emission sources were distinguished, wave-fixed and location-fixed ͑starting with Kemp and Brown, 1983, more recent papers Schneider et al, 1999;Talmadge et al, 1999;Knight and Brass, 2000;Prijs et al, 2000;theoretical foundation: Shera and Guinan, 1999͒. These classes of emissions are also different in that the former is typically associated with nonlinear phenomena, and the latter operates in linear as well as nonlinear models.…”