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 tempora l interactions, as previously reported, may be explained terms of the compr essive non-linearity of the CEOAE input-output (I-O) function. This paper p resents the results of a detailed parametric investigation into such nonlin ear 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, max imum suppression is generally obtained for suppressors presented in advance of test clicks, rather than co-incident with the test clicks. The amount o f advance depends systematically on the two click levels. The measured supp ression 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 dis turbance of the generator elements from their resting state prior to genera tion of the CEOAE. These results may also have general implications relatin g to cochlear responses to transient stimuli and indicate the potential of CEOAEs in probing aspects of cochlear mechanics. (C) 2000 Elsevier Science B.V. All rights reserved.