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Click evoked otoacoustic emissions (CEOAEs), pure-tone audiograms (PTAs), and Bekesy sweep frequency audiograms were recorded from 15 ears of 11 subjects with noise-induced hearing loss. For all ears, hearing threshold levels > or = 30 dB HL were found at the high frequencies. The aims of the study were to examine whether the decomposition of CEOAEs into narrow band components could identify hearing loss in a frequency-specific manner and to what extent audiometric thresholds could be predicted. CEOAEs were parcelled into 0.5-kHz-wide components by means of the wavelet transform. Reproducibility of CEOAE components was compared with audiometric threshold at corresponding frequencies. A general trend of low reproducibility for increasing audiometric thresholds was found. A reproducibility value of 60 per cent was found to best separate normal and elevated thresholds. The presence of a CEOAE component at a given frequency was always associated with audiometric thresholds < or = 20-25 dB HL. On the other hand, the absence of a component was equally associated either with normal or abnormal hearing levels. Large inter-subject variability was observed. A weak linear relationship was found between reproducibility and audiometric thresholds at corresponding frequencies, indicating that analysis of narrow band CEOAE components is valuable for separating normal from hearing-impaired ears but cannot replace the audiogram.

The objective of this study was to investigate the effects of time-windowing on click evoked otoacoustic emissions (CEOAEs); 466 CEOAEs from full-term babies were considered. Data were acquired according to the default ILO88 response window (2.5-20 ms). Because CEOAEs are time-varying signals, each emission was analysed by means of the wavelet transform (WT), a technique which allows a simultaneous representation of the time and frequency features of a signal. By means of the WT it was possible to extract the temporal pattern of the elementary frequency components of the compound emissions. The effects of time-windowing were evaluated on each single emission component: rms and correlation values were computed from six 2.5-ms long time windows in the 2.5-17.5 ms range. Results indicated that both rms and correlation were not constant with time but reached a maximum in specific time-windows, depending on the frequency of the component. For low-frequency components, the correlation typically had a maximum in the interval 10-12.5 ms, whereas high-frequency components had a maximum around 5 ms. Above 12.5 ms, the correlation was greatly decreased for all frequency components. As a result, the comparison between the performance of the default ILO88 window (2.5-20 ms) and the window 2.5-12.5 ms showed that for all frequencies in the 1.5-6 kHz range there was a statistically significant improvement in the correlation. No improvement was observed for frequencies below 1.5 kHz because of their contamination by the residual background noise.

This paper investigated the performance of an optimal bandpass filtering technique to effectively identify click evoked otoacoustic emissions in neonates. The frequency response of the filter was optimized by maximizing the correlation coefficient between two replicate recordings (reproducibility). The optimal cut-off frequencies were also set by controlling the maximum energy loss after filtering to stop the crucial response contents being filtered along with the noise. As an additional constraint, the cut-off frequencies were forced to be outside the range of 1.6 to 4.2 kHz to avoid (in a response identification task) the spontaneous otoacoustic emissions from polarizing the cut-offs and thereby filtering fundamental frequency components, thus leading to an erroneous response classification. The best performance of the optimal filter in terms of increasing the post-filtering reproducibility was obtained when the procedure was applied to recordings whose reproducibility before filtering ranged between 60 and 80 per cent, i.e. for responses classified in most cases as partial pass.

Recordings of emission evoked in response to transient stimuli (TEOAE) are partially contaminated by the initial stimulus artifact. For this reason, a nonlinear estimation method is widely used (derived nonlinear response, DNLR). The aims of this paper are: (1) to analyse some very basic properties of the derived nonlinear emissions such as the short-time input/output relationships; and (2) to show similarities and differences between the classical averaging (linear) and the derived nonlinear recording techniques, in the same ears, both in time and in the frequency domain. At latencies greater than about 6 ms, responses which are recorded using the derived nonlinear technique exhibit no additional features in comparison with linear recordings, at all stimulus levels. At latencies less than 6 ms, the derived nonlinear technique greatly reduces the linear content of the acoustic artifact, and the response may be considered as the initial part of the emission. However, the derived nonlinear responses tend to be considerably noisier than the linear emissions, thus reducing the effectiveness of the technique. The linear responses show a strikingly similar frequency content with respect to the derived nonlinear responses, at least at a high stimulus level and around the main peaks of the spectrum.