The effects of window delay, delinearization, and frequency on tone-burst otoacoustic emission input/output measurements

Magnitude of medial olivocochlear reflex assayed by tone-burst-evoked otoacoustic emissions: reliability and comparison with click-evoked emissions

OBJECTIVE

The purpose of this pilot study was to evaluate the magnitude of the medial olivocochlear reflex (MOCR) estimated by the reduction in tone-burst evoked otoacoustic emissions (TBOAEs) measured at three levels and at three frequencies in response to fixed contralateral white noise. Results were compared with commonly used click-evoked otoacoustic emissions (CEOAEs).

DESIGN

TBOAEs and CEOAEs, with and without contralateral 60 dB SPL white noise, were measured in response to stimulation at 55, 65, and 75 dB peSPL. In each subject, the set of measurements was performed twice. Of particular interest were the MOCR and its repeatability.

STUDY SAMPLE

15 normally hearing persons (13 women, average age 32.3 years, SD = 8.1).

RESULTS

For both CEOAE and TBOAEs, the reliability of the MOCR was much better for broadband measurements than for half-octave-band filtered estimates. At the same time, the reliability of MOCR in half-octave bands was higher for TBOAEs than for CEOAEs, especially at 2 and 4 kHz.

CONCLUSIONS

For general applications where broadband MOCR is of interest, the highest magnitude and reliability is provided by CEOAEs. However, TBOAEs may be better if a particular frequency band is of interest.

Otoacoustic emissions from ears with spontaneous activity behave differently to those without: Stronger responses to tone bursts as well as to clicks

It has been reported that both click-evoked otoacoustic emissions (CEOAEs) and distortion product otoacoustic emissions (DPOAEs) have higher amplitudes in ears that possess spontaneous otoacoustic emissions (SOAEs). The general aim of the present study was to investigate whether the presence of spontaneous activity in the cochlea affected tone-burst evoked otoacoustic emissions (TBOAEs). As a benchmark, the study also measured growth functions of CEOAEs. Spontaneous activity in the cochlea was measured by the level of synchronized spontaneous otoacoustic emissions (SSOAEs), an emission evoked by a click but closely related to spontaneous otoacoustic emissions (SOAEs, which are detectable without any stimulus). Measurements were made on a group of 15 adults whose ears were categorized as either having recordable SSOAEs or no SSOAEs. In each ear, CEOAEs and TBOAEs were registered at frequencies of 0.5, 1, 2, and 4 kHz, and input/output functions were measured at 40, 50, 60, 70, and 80 dB SPL. Global and half-octave-band values of response level and latency were estimated. Our main finding was that in ears with spontaneous activity, TBOAEs had higher levels than in ears without. The difference was more apparent for global values, but were also seen with half-octave-band analysis. Input/output functions had similar growth rates for ears with and without SSOAEs. There were no significant differences in latencies between TBOAEs from ears with and without SSOAEs, although latencies tended to be longer for lower stimulus levels and lower stimulus frequencies. When TBOAE levels were compared to CEOAE levels, the latter showed greater differences between recordings from ears with and without SSOAEs. Although TBOAEs reflect activity from a more restricted cochlear region than CEOAEs, at all stimulus frequencies their behavior still depends on whether SSOAEs are present or not.

Interindividual variation of sensitivity to frequency modulation: its relation with click-evoked and distortion product otoacoustic emissions

The frequency modulation detection limen (FMDL) with a low modulation rate has been used as a measure of the listener's sensitivity to the temporal fine structure of a stimulus, which is represented by the pattern of neural phase locking at the auditory periphery. An alternative to the phase locking cue, the excitation pattern cue, has been suggested to contribute to frequency modulation (FM) detection. If the excitation pattern cue has a significant contribution to low-rate FM detection, the functionality of cochlear mechanics underlying the excitation pattern should be reflected in low-rate FMDLs. This study explored the relationship between cochlear mechanics and low-rate FMDLs by evaluating physiological measures of cochlear functions, namely distortion product otoacoustic emissions (DPOAEs) and click-evoked otoacoustic emissions (CEOAEs). DPOAEs and CEOAEs reflect nonlinear cochlear gain. CEOAEs have been considered also to reflect the degree of irregularity, such as spatial variations in number or geometry of outer hair cells, on the basilar membrane. The irregularity profile could affect the reliability of the phase locking cue, thereby influencing the FMDLs. The features extracted from DPOAEs and CEOAEs, when combined, could account for more than 30 % of the inter-listener variation of low-rate FMDLs. This implies that both cochlear gain and irregularity on the basilar membrane have some influence on sensitivity to low-rate FM: the loss of cochlear gain or broader tuning might influence the excitation pattern cue, and the irregularity on the basilar membrane might disturb the ability to use the phase locking cue.

Reliability of distortion-product otoacoustic emissions and their relation to loudness

The reliability of distortion-product otoacoustic emission (DPOAE) measurements and their relation to loudness measurements was examined in 16 normal-hearing subjects and 58 subjects with hearing loss. The level of the distortion product (L(d)) was compared across two sessions and resulted in correlations that exceeded 0.90. The reliability of DPOAEs was less when parameters from nonlinear fits to the input/output (I/O) functions were compared across visits. Next, the relationship between DPOAE I/O parameters and the slope of the low-level portion of the categorical loudness scaling (CLS) function (soft slope) was assessed. Correlations of 0.65, 0.74, and 0.81 at 1, 2, and 4 kHz were observed between CLS soft slope and combined DPOAE parameters. Behavioral threshold had correlations of 0.82, 0.83, and 0.88 at 1, 2, and 4 kHz with CLS soft slope. Combining DPOAEs and behavioral threshold provided little additional information. Lastly, a multivariate approach utilizing the entire DPOAE I/O function was used to predict the CLS rating for each input level (dB SPL). Standard error of the estimate when using this method ranged from 2.4 to 3.0 categorical units (CU), suggesting that DPOAE I/O functions can predict CLS measures within the CU step size used in this study (5).

Analysis of parameters for the estimation of loudness from tone-burst otoacoustic emissions

There is evidence that tone-burst otoacoustic emissions (TBOAEs) might be useful for estimating loudness. However, within-listener comparisons between loudness and TBOAE measurements are an essential prerequisite to determine appropriate analysis parameters for loudness estimation from TBOAE measurements. The purpose of the present work was to collect TBOAE measurements and loudness estimates across a wide range of levels in the same listeners. Therefore, TBOAEs were recorded for 1- and 4-kHz stimuli and then analyzed using a wide range of parameters to determine which parameter set yielded the lowest mean-square-error estimation of loudness with respect to a psychoacoustical, cross-modality-matching procedure and the inflected exponential (INEX) loudness model. The present results show strong agreement between 1-kHz loudness estimates derived from TBOAEs and loudness estimated using cross-modality matching (CMM), with TBOAE estimation accounting for almost 90% of the CMM variance. Additionally, the results indicate that analysis parameters may vary within a reasonable range without compromising the results (i.e., the estimates exhibit some parametric robustness). The lack of adequate parametric optimization for TBOAEs at 4 kHz suggests that measurements at this frequency are strongly contaminated by ear-canal resonances, meaning that deriving loudness estimates from TBOAEs at this frequency is significantly more challenging than at 1 kHz.

Tone burst-evoked otoacoustic emissions in neonates: normative data

BACKGROUND

Tone-burst otoacoustic emissions (TBOAEs) have not been routinely studied in pediatric populations, although tone burst stimuli have greater frequency specificity compared with click sound stimuli. The present study aimed (1) to determine an appropriate stimulus level for neonatal TBOAE measurements when the stimulus center frequency was 1 kHz, (2) to explore the characteristics of 1 kHz TBOAEs in a neonatal population.

METHODS

A total of 395 normal neonates (745 ears) were recruited. The study consisted of two parts, reflecting the two study aims. Part I included 40 normal neonatal ears, and TBOAE measurement was performed at five stimulus levels in the range 60-80 dB peSPL, with 5 dB incremental steps. Part II investigated the characteristics of the 1 kHz TBOAE response in a large group of 705 neonatal ears, and provided clinical reference criteria based on these characteristics.

RESULTS

The study provided a series of reference parameters for 1 kHz TBOAE measurement in neonates. Based on the results, a suggested stimulus level and reference criteria for 1 kHz TBOAE measures with neonates were established. In addition, time-frequency analysis of the data gave new insight into the energy distribution of the neonatal TBOAE response.

CONCLUSION

TBOAE measures may be a useful method for investigating cochlear function at specific frequency ranges in neonates. However, further studies of both TBOAE time-frequency analysis and measurements in newborns are needed.

Two-tone suppression of stimulus frequency otoacoustic emissions

Stimulus frequency otoacoustic emissions (SFOAEs) measured using a suppressor tone in human ears are analogous to two-tone suppression responses measured mechanically and neurally in mammalian cochleae. SFOAE suppression was measured in 24 normal-hearing adults at octave frequencies (f(p)=0.5-8.0 kHz) over a 40 dB range of probe levels (L(p)). Suppressor frequencies (f(s)) ranged from -2.0 to 0.7 octaves re: f(p), and suppressor levels ranged from just detectable suppression to full suppression. The lowest suppression thresholds occurred for "best" f(s) slightly higher than f(p). SFOAE growth of suppression (GOS) had slopes close to one at frequencies much lower than best f(s), and shallow slopes near best f(s), which indicated compressive growth close to 0.3 dBdB. Suppression tuning curves constructed from GOS functions were well defined at 1, 2, and 4 kHz, but less so at 0.5 and 8.0 kHz. Tuning was sharper at lower L(p) with an equivalent rectangular bandwidth similar to that reported behaviorally for simultaneous masking. The tip-to-tail difference assessed cochlear gain, increasing with decreasing L(p) and increasing f(p) at the lowest L(p) from 32 to 45 dB for f(p) from 1 to 4 kHz. SFOAE suppression provides a noninvasive measure of the saturating nonlinearities associated with cochlear amplification on the basilar membrane.

Inferring basilar-membrane motion from tone-burst otoacoustic emissions and psychoacoustic measurements

The amplitude of otoacoustic emissions, which arise on the basilar membrane, is assumed to be proportional to basilar-membrane motion. It should then be possible to assess basilar-membrane motion on the basis of otoacoustic emissions. The present study provides support for this possibility by comparing basilar-membrane motion inferred from emissions to that inferred from psychoacoustic measures. Three psychoacoustic measurements believed to be associated with basilar-membrane motion were investigated: (1) pulsation threshold; (2) loudness functions derived from temporal integration; and (3) loudness functions derived from loudness matches between pure tones and multitone complexes. Results of the psychoacoustic measurements and of the tone-burst otoacoustic emissions led to very similar estimations of basilar-membrane motion. Accordingly, emissions could serve as an excellent tool--one that is objective, noninvasive, and rapid--for estimating relative basilar-membrane motion.