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

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

Prey recognition and selection by the constant frequency bat, Pteronotus p. parnellii

In the laboratory the neotropical bat, Pteronotus p. parnellii of Jamaica W.I., will readily capture free flying and tethered insects. It will also attack a stationary mechanical insect model when its wing-like parts are rapidly moving. On the basis of our observations we conclude that: (1) P. parnellii are attracted to flying insects and recognition of these rather than background objects is dependent on insect wing movements. Insects which are not beating wings are relatively immune from predation. (2) The frequency of the wingbeats of the insects is important in prey recognition. P. parnellii are not attracted to insects or to mechanical models of insects when the wing movements are slow. (3) These bats are selective in the acquisition of their prey and not simply opportunistic. They ignore or reject lampyrid beetles, arctiid and ctenuchid moths and the geometrid moth, Thyrinteina arnobia. They consume a variety of other Lepidoptera, Coleoptera, and insects from other orders. Their prey consists of both large and small insects. (4) In spite of the emission of intense sonar pulses with a constant frequency component of long duration, they can effectively hunt their prey in relatively confined spaces. They can chase their prey among simple arrays of obstacles and they can pursue insects to within several centimeters of large obstacles. (5) Evidence supports the hypothesis that the basis for insect wingbeat detection is the rapid and repetitive pattern of Doppler-shifts which the beating wings impose on the echoes of the constant frequency component of the bat\u27s pulses