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 nonlinear temporal interactions between the test and suppressor clicks and/or the CEOAEs they evoke. There are some discrepancies amongst previous reports of the phenomenon, and the underlying mechanisms are not understood. In particular, it is unclear whether the suppression reported simply reflects the compressive nonlinearity of the CEOAE input-output (I-O) function. This paper presents a simple model of the nonlinear interactions between CEOAEs evoked by two closely-spaced clicks. The model shows that suppression as reported may be entirely derived from CEOAE I-O nonlinearity, in combination with the extended duration of the cochlear responses to click stimuli. It is also shown experimentally that suppression is insensitive to the polarities of test and suppressor clicks, which is consistent with the model based on I-O nonlinearity. A companion paper (Kapadia and Lutman, Hear. Res. 146 (2000)) presents experimental findings from a detailed parametric study of nonlinear temporal interactions in CEOAEs in human subjects with normal hearing. 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 nonlinear interactions.