Frequency analysis of the contralateral suppression of evoked otoacoustic emissions by narrow-band noise.

The influence of noise bandwidth on the contralateral masking of click-evoked otoacoustic emissions was investigated by recording emissions from 20 normal subjects with contralateral narrow-band noise, with wide-band noise and without contralateral noise for comparison. Narrow-band noise of five different centre frequencies and three different bandwidths per frequency was used at intensities of 40 and 60 dB SL. Analysis of the emissions showed that the 40-dB SL contralateral noise did not produce a significant amount of suppression. The suppression produced by 60-dB SL noise was spread throughout the frequency range of the emissions, with limited frequency specificity. There was some evidence that the amount of suppression increases with the bandwidth of the noise, particularly for noises centred on 1 and 2 kHz; the wide-band noise produced much greater suppression than any of the narrow bands. There was a large amount of inter-subject variation, which could not be explained by differences in the absolute level of the emissions. One subject with a total unilateral hearing loss in the contralateral ear was also tested, and gave no significant suppression.