INVOLVEMENT OF THE OLIVOCOCHLEAR BUNDLE IN THE DETECTION OF TONES IN NOISE

To investigate the involvement of auditory efferents in hearing-in-noi se in humans, olivocochlear bundle (OCB) functioning and detection-in- noise abilities were compared in 30 subjects. OCB function was assesse d in terms of contralateral attenuation of evoked otoacoustic emission s (EOAE): i.e., the reduction in EOAE amplitude elicited by a 30-dB SL contralateral broadband noise. Correspondingly, the detection thresho lds for 1- and 2-kHz tone pips embedded in 50-dB SPL broadband noise w ere measured in the same ear as the EOAEs, successively in the presenc e and in the absence of a 30-dB SL broadband noise in the opposite ear . The shifts in detection threshold induced by the contralateral stimu lation could thus be compared to those in EOAEs. The results indicated significant statistical correlations between the contralateral attenu ation of EOAEs and (1) the detection threshold of the 2-kHz signal and (2) the contralaterally induced shift in the 1- and 2-kHz thresholds. Furthermore, the correlation between contralaterally induced reductio n of EOAE amplitude and contralaterally induced threshold shift was ob served only in the group of subjects who had first performed the detec tion task in the presence of contralateral stimulation. These results, which suggest that OCB is involved in detection of tones in noise in humans, are discussed in relation to previous physiological and behavi oral studies of OCB function. (C) 1996 Acoustical Society of America.