MECHANISMS OF ACOUSTIC PERCEPTION AND ORIENTATION

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Behavioral, physiological and anatomical methods will be employed to investigate the biosonar system of the Doppler-shift compensating bat, Pteronotus p. parnellii. Echolocative behavior will be analyzed in animals pursuing and capturing prey and during simulated (pendulum) flight. Attention will be directed to amplitude as well as Doppler-shift compensation and to analysis of the ways basic signal parameters (CF, FM and harmonics) change in different echolocative situations. Computer assisted analysis will be utilized to study changing signal parameters in microphone as well as cochlear microphonic potential records obtained with chronically implanted electrodes and with a microminiature radiotelemetry system. These data will be used to assess existing theories of echolocation, to establish the response characteristics of the ear under actual echolocative conditions and to gain knowledge about the complex types of stimulus conditions that the ear normally encounters. The structure of the cochlea, and especially elements associated with mechanical vibrations, fine frequency analysis and the unusual resonance properties of the ear will be studied with light and scanning and transmission electron microscopy. Quantitative data will be obtained from serial sections in order to assess morphologic properties in different regions of the cochlea and to correlate structures in different regions with frequency maps of the cochlea. The major long term goals of this investigation are to study biosonar signal design and signal processing at peripheral and central levels and to demonstrate some of the ways in which the mammalian cochlea has been modified to meet unusual sensory demands. Experiments will be designed to show that fine tuning at the receptor level has been accomplished by changing the arrangement of the vibratory elements and/or their sensory processes, or through changes in mechanical or biochemical support systems. The information from this study will be useful for understanding many basic bioacoustic phenomena and for technological advances in the areas of acoustic signal processing and radiotelemetry. Knowledge of the mechanisms underlying these systems may prove useful in the further development of navigational aids for the blind and for acoustic imaging.