Temporal suppression of long-latency click-evoked otoacoustic emissions

A comprehensive set of results from double click suppression experiments on otoacoustic emissions (OAEs) have been presented by Hine and Thornton [1] and Kapadia and Lutman [2]. They found that suppression of a click-evoked otoacoustic emission (CEOAE) varied with the timing and level of a suppressor-click presented close in time to the test-click. Maximal suppression was found when the suppressor-click led the test-click by 2-4 ms. The double click suppression experiment set out by Hine and Thornton was repeated here and the analysis extended to the 'long-latency' CEOAE (duration > 20 ms) whereas previous studies only focused on the 'short-latency' CEOAE (duration < 20 ms). The hypothesis was that suppression would continue over the long-latency CEOAE since this region is probably dominated by spontaneous OAEs (SOAEs) synchronising with the click stimulus. The results for two exemplary subjects showed that the nonlinear suppression effect remained on the long-latency CEOAE, indicating that both SOAEs and CEOAEs originate from the same cochlear nonlinearities, as earlier suggested by Kemp and Chum [3]. The apparent similar origin of both types of emissions implies that the same temporal effects influence their responses.