On the spectral periodicity of transient-evoked otoacoustic emissions fromnormal and damaged cochleas

The spectral quasi-periodicity of transient-evoked otoacoustic emissions (T EOAE) is well acknowledged since Zwicker described a preferred spacing of 0 .4 bark between consecutive peaks in the spectrum of otoacoustic emissions from normal ears. While there is scarce evidence of any anatomical reason f or this regularity, several functional models of the cochlea have predicted that the structure of emission spectra reflects important characteristics of cochlear filters. In an attempt to check such predictions, the average r egularity of TEOAE spectra was studied in three groups of human subjects, n ormally hearing adults, healthy neonates, and adults suffering from noise-i nduced hearing loss. Significant differences in emission periodicities were found. Around 1 kHz, the preferred spacing was close to 130 Hz in normally hearing adult ears and neonates. In contrast, no clear periodicity was fou nd in the group of damaged ears, even though they had clinically normal pur e-tone audiometry below 2 kHz. Around 4 kHz, the preferred spacing was clos e to 240 Hz in normal adults and neonates, whereas TEOAEs were absent in ma ny impaired ears. A phenomenological model assuming that TEOAEs stem from t he responses of a slightly disarrayed bank of highly tuned filters predicts that the filter width would be the same in healthy young adults and neonat es. In contrast, ears suffering from high-frequency hearing loss could exhi bit early damaged filters. The proposed method might provide an objective a ssessment of parameters otherwise difficult to evaluate: especially in neon atal cochleas. (C) 2000 Acoustical Society of America. [S0001-4966(00)04209 -0].