[Otoacoustic emission cochleogram evoked by bone conducted stimulation].

As bone conducted stimulation, tone bursts of different frequencies were applied through the forehead in 7 normal-hearing subjects. Binaural evoked otoacoustic emissions (EOAE) were then recorded simultaneously, which saved one half of the time required for conventional monaural recording. Analysed with autoregressive modeling, the main echo of EOAE was a narrow-band sound with a stimulus dependent central frequency. It was suggested that the generation site of EOAE was near to that cochlear portion stimulated by the corresponding frequency. The latency of EOAE, although independent of the stimulus intensity, tended to be shorter at higher stimulus frequencies. This was possibly due to the differences in the distances from the generation sites of the otoacoustic emissions to the tympanic membrane. Recordable otoacoustic emissions were evoked by tone bursts of 1.0, 2.0, 3.0 and 4.0 kHz in all the 14 normal ears except one at 4.0 kHz, and 10 and 7 ears by tone bursts of 0.5 and 6.0 kHz, respectively. Emission cochleogram was obtained when the means of EOAE detection thresholds were plotted in an audiogram format. The lowest threshold was found at 1.0 kHz. This might be related to the middle ear resonance frequency of 1100 +/- 230 Hz. The technique of simultaneous recording of binaural EOAE and plotting of emission cochleogram described in this paper is clinically useful as a means of objective evaluation of hearing.