Nonlinear temporal interactions in click-evoked otoacoustic emissions. II. Experimental data.

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. A model described in a companion paper (Kapadia and Lutman, Hear. Res. 146 (2000) 89-100) shows that such nonlinear temporal interactions, as previously reported, may be explained in terms of the compressive non-linearity of the CEOAE input-output (I-O) function. This paper presents the results of a detailed parametric investigation into such nonlinear interactions, studied in 12 normal adult ears over a wide range of test and suppressor click levels and inter-click intervals. The results differ from those generated by the model in a number of respects. Principally, maximum suppression is generally obtained for suppressors presented in advance of test clicks, rather than co-incident with the test clicks. The amount of advance depends systematically on the two click levels. The measured suppression can also exceed the theoretical maximum allowed by the model. It is concluded that the nonlinear temporal interactions measured do not simply reflect CEOAE I-O function non-linearity. They may, instead, arise from disturbance of the generator elements from their resting state prior to generation of the CEOAE. These results may also have general implications relating to cochlear responses to transient stimuli and indicate the potential of CEOAEs in probing aspects of cochlear mechanics.