Simultaneous suppression of tone burst-evoked otoacoustic emissions – Effect of level and presentation paradigm

There is conflict in the literature over whether individual frequency components of a transient-evoked otoacoustic emission (TEOAE) are generated within relatively independent "channels" along the basilar membrane (BM), or whether each component may be generated by widespread areas of the BM. Two previous studies on TEOAE suppression are consistent with generation within largely independent channels, but with a degree of interaction between nearby channels. However, both these studies reported significant suppression only at high stimulus levels, at which the "nonlinear" presentation paradigm was used. The present study clarifies the separate influences of stimulus level and presentation paradigm on this type of suppression. TEOAEs were recorded using stimulus tone bursts at 1, 2 and 3 kHz and a complex stimulus consisting of a digital addition of the three tone bursts, over a range of stimulus levels and both "linear" and "nonlinear" presentation paradigms. Responses to the individual tone bursts were combined offline and compared with responses to the complex stimuli. Results clearly demonstrate that TEOAE suppression under these conditions is dependent upon stimulus level, and not upon presentation paradigm. It is further argued that the data support the "local" rather than "widespread" model of TEOAE generation, subject to nonlinear interactions between nearby generation channels.