Volume 134, Issue 1, July 2013
Index of content:
- PHYSIOLOGICAL ACOUSTICS 
Wideband energy reflectance measurements: Effects of negative middle ear pressure and application of a pressure compensation procedure134(2013); http://dx.doi.org/10.1121/1.4807509View Description Hide Description
The wideband energy reflectance (ER) technique has become popular as a tool for evaluating middle ear function. Negative middle ear pressure (MEP) is a prevalent form of middle ear dysfunction, which may impact application of ER measurements in differential diagnosis. A negative MEP may be countervailed by application of an equivalent negative ear canal pressure. The present study examined ER in the same ears under normal and experimentally induced negative MEP conditions. Thirty-five subjects produced at least one negative MEP each (−40 to −225 daPa). Negative MEP significantly altered ER in a frequency-specific manner that varied with MEP magnitude. ER increased for low- to mid-frequencies with the largest change (∼0.20 to 0.40) occurring between 1 and 1.5 kHz. ER decreased for frequencies above 3 kHz with the largest change (∼–0.10 to –0.25) observed between 4.5 and 5.5 kHz. Magnitude of changes increased as MEP became more negative, as did the frequencies at which maximum changes occurred, and the frequency at which enhancement transitioned to reduction. Ear canal pressure compensation restored ER to near baseline values. This suggests that the compensation procedure adequately mitigates the effects of negative MEP on ER. Theoretical issues and clinical implications are discussed.
134(2013); http://dx.doi.org/10.1121/1.4809676View Description Hide Description
Distortion-product otoacoustic emissions (DPOAEs) were measured in rabbits as time waveforms by employing a phase-rotation technique to cancel all components in the final average, except the 2f 1-f 2 DPOAE. Subsequent filtering allowed the DPOAE waveform to be clearly visualized in the time domain. In most conditions, f 2 was turned off for 6 ms, which produced a gap so that the DPOAE was no longer generated. These procedures allowed the DPOAE onset as well as the decay during the gap to be observed in the time domain. DPOAEs were collected with L 1 = L 2 = 65-dB sound pressure level primary-tone levels for f 2/f 1 ratios from 1.25 to 1.01 in 0.02 steps. Findings included the appearance of complex onsets and decays for the DPOAE time waveforms as the f 2/f 1 ratio was decreased and the DPOAE level was reduced. These complexities were unaffected by interference tones (ITs) near the DPOAE frequency place (f dp), but could be removed by ITs presented above f 2, which also increased DPOAE levels. Similar outcomes were observed when DPOAEs were measured at a sharp notch in the DPOAE level as a function of the f 2 primary tone frequency, i.e., DP-gram. Both findings were consistent with the hypothesis that the DPOAE-ratio function, and some notches in the DP-gram, are caused by interactions of distributed DPOAE components with unique phases.
134(2013); http://dx.doi.org/10.1121/1.4807505View Description Hide Description
Although stimulus-frequency otoacoustic emissions (SFOAEs) offer compelling advantages as noninvasive probes of cochlear function, they remain underutilized compared to other evoked emission types, such as distortion-products (DPOAEs), whose measurement methods are less complex and time-consuming. Motivated by similar advances in the measurement of DPOAEs, this paper develops and characterizes a more efficient SFOAE measurement paradigm based on swept tones. In contrast to standard SFOAE measurement methods, in which the emissions are measured in the sinusoidal steady-state using discrete tones of well defined frequency, the swept-tone method sweeps rapidly across frequency (typically at rates of 1 Hz/ms or greater) using a chirp-like stimulus. Measurements obtained using both swept- and discrete-tone methods in an interleaved suppression paradigm demonstrate that the two methods of measuring SFOAEs yield nearly equivalent results, the differences between them being comparable to the run-to-run variability encountered using either method alone. The match appears robust to variations in measurement parameters, such as sweep rate and direction. The near equivalence of the SFOAEs obtained using the two measurement methods enables the interpretation of swept-tone SFOAEs within existing theoretical frameworks. Furthermore, the data demonstrate that SFOAE phase-gradient delays—including their large and irregular fluctuations across frequency—reflect actual physical time delays at different frequencies, showing that the physical emission latency, not merely the phase gradient, is inherently irregular.
134(2013); http://dx.doi.org/10.1121/1.4807560View Description Hide Description
The aim of this study is to further explore the relationship between distortion-product otoacoustic emission (DPOAE) measurements and categorical loudness scaling (CLS) measurements using multiple linear regression (MLR) analysis. Recently, Thorson et al. [J. Acoust. Soc. Am. 131, 1282–1295 (2012)] obtained predictions of CLS loudness ratings from DPOAE input/output (I/O) functions using MLR analysis. The present study extends that work by (1) considering two different (and potentially improved) MLR models, one for predicting loudness rating at specified input level and the other for predicting the input level for each loudness category and (2) validating the new models' predictions using an independent set of data. Strong correlations were obtained between predicted and measured data during the validation process with overall root-mean-square errors in the range 10.43–16.78 dB for the prediction of CLS input level, supporting the view that DPOAE I/O measurements can predict CLS loudness ratings and input levels, and thus may be useful for fitting hearing aids.
A comparison of spectral magnitude and phase-locking value analyses of the frequency-following response to complex tones134(2013); http://dx.doi.org/10.1121/1.4807498View Description Hide Description
Two experiments, both presenting diotic, harmonic tone complexes (100 Hz fundamental), were conducted to explore the envelope-related component of the frequency-following response (FFRENV), a measure of synchronous, subcortical neural activity evoked by a periodic acoustic input. Experiment 1 directly compared two common analysis methods, computing the magnitude spectrum and the phase-locking value (PLV). Bootstrapping identified which FFRENV frequency components were statistically above the noise floor for each metric and quantified the statistical power of the approaches. Across listeners and conditions, the two methods produced highly correlated results. However, PLV analysis required fewer processing stages to produce readily interpretable results. Moreover, at the fundamental frequency of the input, PLVs were farther above the metric's noise floor than spectral magnitudes. Having established the advantages of PLV analysis, the efficacy of the approach was further demonstrated by investigating how different acoustic frequencies contribute to FFRENV, analyzing responses to complex tones composed of different acoustic harmonics of 100 Hz (Experiment 2). Results show that the FFRENV response is dominated by peripheral auditory channels responding to unresolved harmonics, although low-frequency channels driven by resolved harmonics also contribute. These results demonstrate the utility of the PLV for quantifying the strength of FFRENV across conditions.