Temporal dynamics of the generator of stimulated otoacoustic emissions

Abstract

The early emission work of David Kemp investigated temporal properties of click-evoked otoacoustic emissions (CEOAEs). Suppressor clicks were positioned up to 10 ms before or after the evoking (test) click and reduced the emission amplitude. Intriguingly, suppressors that preceded the test click by 1-2 ms were more effective than simultaneously presented suppressors. This observation seems not to support the hypothesis that emission generation operates on the basis of an instantaneous gain/suppression mechanism, for which simultaneously presented suppressors should be most effective. Kemps’ observations thus left the field with an important OAE generation question that inspired several OAE studies. Kemps’ results can be explained on the basis of (i) a non-instantaneous gain mechanism at the OAE generation site, or (ii), complex temporal interactions of basilar-membrane impulse responses (BM IRs) that operate with an instantaneous nonlinearity, but yield the observed non-instantaneous suppression properties. We investigated these dynamics using a nonlinear transmission-line model of the human cochlea and found that maximal CEOAE suppression can occur for preceding clicks even when the cochlear nonlinearity is kept time-invariant, supporting hypothesis (ii). Additionally, we used the frequency-dependence of CEOAE suppression to quantify human BM IR duration and cochlear filter tuning, yielding QERB estimates of 13.8 F[in kHz]0.22.The early emission work of David Kemp investigated temporal properties of click-evoked otoacoustic emissions (CEOAEs). Suppressor clicks were positioned up to 10 ms before or after the evoking (test) click and reduced the emission amplitude. Intriguingly, suppressors that preceded the test click by 1-2 ms were more effective than simultaneously presented suppressors. This observation seems not to support the hypothesis that emission generation operates on the basis of an instantaneous gain/suppression mechanism, for which simultaneously presented suppressors should be most effective. Kemps’ observations thus left the field with an important OAE generation question that inspired several OAE studies. Kemps’ results can be explained on the basis of (i) a non-instantaneous gain mechanism at the OAE generation site, or (ii), complex temporal interactions of basilar-membrane impulse responses (BM IRs) that operate with an instantaneous nonlinearity, but yield the observed non-instantaneous suppression propertie...