Otoacoustic Emissions Evoked by Two-Tone Bursts Using Linear and Non-Linear Protocol

Otoacoustic emissions (OAEs) were recorded for tone bursts presented separately and as a two-tone burst complex. Signals were delivered at 70 dB SPL using a non-linear processing method and at 60 dB SPL using a linear method. Two types of stimuli were applied to record tone burst OAEs (TBOAEs): (a) cosine-windowed tone bursts of 5-ms duration with center frequencies of 1, 1.5, 2 and 3 kHz, (b) complex stimuli consisting of a digital addition of the 1-kHz tone burst together with either the 1.5-, 2- or 3-kHz tone burst. Recorded signals were processed using the method of adaptive approximations by matching pursuit (MP). The MP method allowed decomposition of signals into waveforms of defined frequency, latency, time span, and amplitude. This approach provided a high time-frequency (t-f) resolution and identified patterns of resonance modes that were characteristic for TBOAEs recorded in each ear. The effect of suppression was statistically significant only for the 1, 1.5-kHz condition and slightly greater for the non-linear mode than for the linear mode. For the dual stimulation by 1 and 1.5-kHz, the MP revealed the existence of closely positioned resonance modes associated with responses recorded individually with the stimuli differing in frequency by 500 Hz. The comparison of t-f distributions calculated for dual (two-tone bursts) and sum-of-singles conditions exhibited mutual suppression of resonance modes common to both stimuli