Suppression of tone burst evoked otoacoustic emissions in relation to frequency separation

Tone burst evoked otoacoustic emissions (TBEOAEs) were measured for two ton e bursts presented separately and as a two-tone burst complex to examine th e linearity of TBEOAE generators for different frequency separations of the stimuli. The stimuli were: (a) tone bursts of 5-ms duration and center fre quencies of 1, 1.5, 2 and 3 kHz; (b) complex stimuli with the 1-kHz tone bu rst combined digitally with each of the other specified tone bursts. Signal s were delivered at 70 dB SPL using a non-linear processing method and at 6 0 dB SPL using a linear method to 21 ears of normally hearing adults. Spect ra of TBEOAEs obtained with single-tone bursts were superimposed (composite ) and compared to those of the two-tone burst complex. A close corresponden ce between the composite and complex spectra was present in all ears. Howev er, the components on the higher-frequency slope of the 1-kHz spectral peak were reduced in the complex spectra obtained with a frequency separation o f 0.5 kHz when compared to the corresponding composite spectra. The reducti on was greater at a stimulus level of 70 dB SPL than with 60 dB SPL. The ef fect was smaller for a frequency separation of 1 kHz, and almost absent for the tone burst separation of 2 kHz. Thus, suppression leads to weak non-li near frequency superposition for higher-level., closely spaced stimuli. (C) 2000 Elsevier Science B.V. All rights reserved.