A tone burst-evoked otoacoustic emission (TBOAE) can be suppressed by the simultaneous presentation of an additional higher frequency tone burst (Yoshikawa et al, 2000; Killan et al, 2012). This simultaneous suppression of TBOAEs (SSTBOAEs) has been explained in terms of a local nonlinear interaction (LNI)-based mechanism (Killan et al, 2012). This states that SSTBOAEs results from local interactions between the basilar membrane vibration patterns caused by each tone burst. These interactions are assumed to be governed by the compressive amplitude nonlinearity exhibited by the TBOAE response. However, there is doubt whether this mechanism can account for SSTBOAEs caused by two additional higher frequency tone bursts. Whilst a simple additive effect is predicted by the LNI-based mechanism (so that more suppression is caused by the three-tone burst combination compared to the two-tone burst combination), comparison of suppression values reported across three separate studies suggests that the opposite is true. There are two possible explanations for this difference: (i) it simply reflects methodological and subject differences across the three studies (none of which tested both two- and three-tone burst combinations), or (ii) it implies that more complex interactions, different to those assumed in the LNI-based mechanism, are involved for the three-tone burst combination. In order to understand which of these alternatives is most likely, SSTBOAEs was measured for two and three-tone burst combinations from thirteen normal ears. Prior to this, predictions were obtained from a model of the LNI-based mechanism described by Killan et al (2012). Model predictions and TBOAE measurements were made that allowed suppression to be calculated (in the region of 1 kHz) for combinations of tone bursts with centre frequencies of 1 and 2 kHz, 1 and 3 kHz and 1, 2 and 3 kHz. Model predictions confirmed the additive suppression effect expected with the LNI-based mechanism, with the three-tone burst combination causing greater suppression than the two-tone burst combination. Comparison of SSTBOAEs across two and three-tone burst combinations revealed a similar additive suppression effect. It is therefore concluded that SSTBOAEs caused by three-tone burst combinations is governed by the same LNI-based mechanism used to account for two-tone burst suppression. The differences apparent across previous studies were most likely accounted for by methodological and subject differences.
CORE (COnnecting REpositories)
CORE (COnnecting REpositories)