Ipsilateral suppression effects on transient evoked otoacoustic emission.

The spectral properties of click- and tone-evoked otoacoustic emission (OAE) under ipsilateral simultaneous tonal masking conditions as well as the changes of click-evoked OAE under ipsilateral forward masking by clicks were studied in normal-hearing subjects. It was found that (i) transiently evoked OAE (TEOAE) spectra consist of a number of peaks individual to the subject and distributed along a sufficiently wide cochlear region; (ii) each spectral peak is excited only when the stimulus energy was concentrated within the frequency range covering the frequency of the particular peak; (iii) different TEOAE spectral peaks can be masked independently under simultaneous tonal masking conditions; (iv) the TEOAE tuning curve shape is more closely related to the spectrum of TEOAE but not to that of the stimulus; (v) forward masking of TEOAE generation is most pronounced during the first few milliseconds after masker click onset and become significantly smaller with the longer latency. It is suggested that: (i) TEOAE is generated by a number of local generators individually distributed along the cochlear partition within a sufficiently wide region and characterized by different power; (ii) possible efferent effects in the ipsilateral TEOAE suppression are negligible as compared to the TEOAE reduction of exclusively cochlear origin.