Optimizing swept-tone protocols for recording distortion-product otoacoustic emissions in adults and newborns

Abstract

Distortion-product otoacoustic emissions (DPOAEs), which are routinely used in the audiology clinic and research laboratory, are conventionally recorded with discrete tones presented sequentially across frequency. However, a more efficient technique sweeps tones smoothly across frequency and applies a least-squares-fitting (LSF) procedure to compute estimates of otoacoustic emission phase and amplitude. In this study, the optimal parameters (i.e., sweep rate and duration of the LSF analysis window) required to record and analyze swept-tone DPOAEs were tested and defined in 15 adults and 10 newborns. Results indicate that optimal recording of swept-tone DPOAEs requires use of an appropriate analysis bandwidth, defined as the range of frequencies included in each least squares fit model. To achieve this, the rate at which the tones are swept and the length of the LSF analysis window must be carefully considered and changed in concert. Additionally, the optimal analysis bandwidth must be adjusted to accommodate frequency-dependent latency shifts in the reflection-component of the DPOAE. Parametric guidelines established here are equally applicable to adults and newborns. However, elevated noise during newborn swept-tone DPOAE recordings warrants protocol adaptations to improve signal-to-noise ratio and response quality.

Changes in the Compressive Nonlinearity of the Cochlea During Early Aging: Estimates From Distortion OAE Input/Output Functions

“…A sweep rate of 0.5 octaves/second with an LSF analysis window of 125 ms was used for f 2 = 1–4 kHz, yielding an analysis bandwidth of 0.06 octaves across frequency which has shown to be an optimal combination of parameters (Abdala et al 2015). For f 2 = 4–8 kHz, the DPOAE was analyzed with an LSF window of 500 ms.…”

Probing apical-basal differences in the human cochlea using distortion-product otoacoustic emission phase

“…The DPOAE responses at the f dp frequency were estimated by minimizing the squared error between a model of the response and the average of recorded responses which were not classified as noisy (similar to [3]). The effective stimulus pressures were estimated as well to verify the calibration and to enable the calculation of the DPOAE phase with reference to that of the stimuli, as in ϕ dp = ϕ measured −(2 ϕ 1 − ϕ 2 ).…”

Frequency shifts in distortion-product otoacoustic emissions evoked by swept tones

“…In contrast to traditional discrete-tone methods, in which different frequency components of the otoacoustic emission (OAE) are measured stepwise in the sinusoidal steady state, swept-tone techniques smoothly traverse the full frequency range of interest, often at rates exceeding 1 octave per second. Although swept-tone methods generally yield estimates of OAE amplitude and phase that closely match those obtained with discrete tones (e.g., Long et al, 2008;Kalluri and Shera, 2013;Abdala et al, 2015), systematic differences are sometimes apparent. For example, distortion-product otoacoustic emission (DPOAE) fine structure-the pattern of spectral ripples that results from alternating constructive and destructive interference between the reflection and distortion components of the total DPOAE-has been found to shift to the right or to the left-that is, either upward or downward in frequency, in the same direction as the sweep-by amounts that vary somewhat idiosyncratically from subject to subject but appear to depend systematically on the sweep rate (Henin et al, 2011;AlMakadma et al, 2015;Abdala et al, 2015).…”

“…P "# dp ðf Þ and P "# d ðf Þ are obtained from the time-domain sweep waveforms using narrow-and wideband LSF analysis, respectively. Details of the LSF analysis, including the effects of varying the bandwidth, are described elsewhere (Abdala et al, 2015(Abdala et al, , 2016. To quantify the local similarity between the fine-structure patterns F " and F # as a function of frequency shift (or "lag"), Df , we compute the windowed (or moving) cross-correlation at frequency f: …”

“…For the numerical computations, signals were sampled at 48 kHz. Emissions were extracted from the sweptfrequency signals using least-squares fitting (e.g., Long et al, 2008;Kalluri and Shera, 2013;Abdala et al, 2015). Figure 2 shows the resulting DPOAE levels in a narrow frequency region centered on 2 kHz, the location of a finestructure peak in the steady-state spectrum.…”