Frequency-specific information from click evoked otoacoustic emissions in noise-induced hearing loss

Click evoked otoacoustic emissions (CEOAEs), purl-tone audiograms (PTAs), a nd Bekesy sweep frequency audiograms were recorded from 15 ears of 11 subje cts with noise-induced hearing loss. For all ears, hearing threshold levels greater than or equal to 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 transf orm. Reproducibility of CEOAE components was compared with audiometric thre shold 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 w ith audiometric thresholds less than or equal to 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 narro w band CEOAE components is valuable for separating normal from hearing-impa ired ears but cannot replace the audiogram.