EFFECT OF CONTRALATERAL ACOUSTIC STIMULATION ON THE GROWTH OF CLICK-EVOKED OTOACOUSTIC EMISSIONS IN HUMANS

Input-output (I/O) functions of click-evoked otoacoustic emissions (CE OAEs) were obtained over a 12 dB range for 64 normally hearing adult l isteners with and without contralateral broadband noise (BBN). Contral ateral acoustic stimulation (GAS) is a convenient way of suppressing r esponses to ipsilateral stimuli, probably acting via the medial olivoc ochlear system (MOCS). The present study shows that this contralateral sound suppression of CEOAEs is largest at low stimulus levels. In fac t, the curves obtained under CAS approach the curves obtained without CAS as stimulus level rises. I/O slope analysis for the whole study po pulation (n = 64) showed a slight but significant rise in slope with B BN, which may be interpreted as I/O function decompression. A loss of contralateral suppression effect at high ipsilateral stimulus levels w as found in both very low and very high amplitude CEOAE subjects, desp ite the fact that I/O slopes differed between these two groups, wherea s rise in slope under contralateral stimulation failed to be found for these same 2 groups of 16 subjects each. These findings clearly indic ate that the MOCS is mostly functional at low sound levels, and sugges t that the study of CEOAE I/O slope alteration under CAS may help spec ify one form of MOCS action on cochlear functioning.