Nonlinear temporal interactions in click-evoked otoacoustic emissions. I. Assumed model and polarity-symmetry

Click-evoked otoacoustic emissions (CEOAEs) are reduced in amplitude by the presentation of 'suppressor' clicks that either closely lead or follow the stimulus ('test') clicks. This suppression of the response represents nonl inear temporal interactions between the test and suppressor clicks and/or t he CEOAEs they evoke. There are some discrepancies amongst previous reports of the phenomenon, and the underlying mechanisms are not understood. In pa rticular: it is unclear whether the suppression reported simply reflects th e compressive nonlinearity of the CEOAE input-output (I-O) function. This p aper presents a simple model of the nonlinear interactions between CEOAEs e voked by two closely-spaced clicks. The model shows that suppression as rep orted may be entirely derived from CEOAE I-O nonlinearity, in combination w ith the extended duration of the cochlear responses to click stimuli. It is also shown experimentally that suppression is insensitive to the polaritie s of test and suppressor clicks, which is consistent with the model based o n I-O nonlinearity. A companion paper (Kapadia and Lutman, Hear. Res. 146 ( 2000)) presents experimental findings from a detailed parametric study of n onlinear temporal interactions in CEOAEs in human subjects with normal hear ing. The findings are compared with the pattern of results generated by the above model, in order to assess the role of I-O nonlinearity in these nonl inear interactions. (C) 2000 Elsevier Science B.V. All rights reserved.