Arbeitsgruppe Medizinische Phys., Fachbereich Phys., Carl-von-Ossietzky Univ., D-26111 Oldenburg, Germany
The influence of additional continuous tones on transiently evoked otoacoustic emissions (TEOAE) is studied with normal hearing subjects. If a single continuous tone is present, nearby frequency components of the TEOAE are synchronized to this tone in a similar way as spontaneous OAE can be synchronized. This effect can be deducted from the reduction (``suppression'') of the corresponding OAE component since the additional continuous tone is designed to exhibit a phase shift of pi between successive averaging frames and thus cancels out. To suppress several spectral components of the TEOAE, a continuous tone complex was employed. The frequency difference between adjacent components of this tone complex yields an optimum value at about a critical bandwidth. An application of these findings is the stimulation and evaluation of TEOAE from a predefined region on the basilar membrane: While the frequency range of the evoking signal can be limited by using chirp stimuli (i.e., short frequency sweeps), the TEOAE components outside this frequency range can be suppressed by using an appropriate set of suppressor tones.