Entwicklung verbesserter Verfahren audiologischer Diagnostik zur objektiven Charakterisierung von Hoerschaeden und zur Frueherkennung des vulnerablen Innenohres Schlussbericht

Abstract

Distortion product otoacoustic emissions (DPOAE) are generated undoubted in the region of overlap between the two travelling waves of primaries f_1 and f_2 (primary generator). Since DPOAE lead to a psychoacoustic preception, it is suspected that the cochlear amplifier is additionally activated at place 2f_1-f_2 (secondary generator) leading to a stimulus frequency emission (SFOAE). In suppression experiments we demonstrated that a suppressor tone, 25 Hz above the frequency of the postulated secondary generator, alters DP-amplitude depending (1.) on the DP-gram fine structure and (2.) the sound pressure level of the suppressor (-20 to 80 dB SPL). At a maximum of the fine structure low suppressor levels (<50 dB SPL) reduced the DP-amplitude, whereas an increase occurred at a minimum. Intermediate suppressor levels (50-60 dB SPL) always clamped the DP-amplitude and extinguished the DP-gram fine structure. Our results support the hypothesis that conventional DPOAE, which are measured in the external ear canal, are evoked from the primary and secondary generator. Depending on the relative phase between the two emissions, a constructive resp. destructive interference of the two signals results in an emission pattern, which closely resembles the DP-gram fine structure. When the secondary generator is suppressed by intermediate suppressor levels DPOAE amplitude depends only from the status of the cochlear amplifier near f_2. These emissions, which we call 'single generator' DPOAE (sgDPOAE) may show a closer correlation to auditory threshold. (orig.)SIGLEAvailable from TIB Hannover: DtF QN1(58,42) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany)DEGerman