SOUND EMISSION FROM COCHLEAR FILTERS AND FOVEAE - DOES THE AUDITORY SENSE ORGAN MAKE SENSE

Sense organs filter relevant information from a broad background of ph ysical interactions and dis card possible perceptual input that has no t proven useful during the course of biological evolution. Sense organ s not only limit the access to physical reality, under certain conditi ons they have a life of their own and produce responses even in the ab sence of physical stimulation. As a perfect example, the inner ear, th e cochlea, in addition to detecting incoming sound waves, it also is c apable of producing sound energy. Such ''active'' processes, however, seem to be necessary to push detection thresholds close to physical li mits. The price that has to be paid are ''cochlear artifacts'' like ot oacoustic emissions. In the following, measurement of sound that is em itted by the ear will be introduced as a noninvasive means to assess c ochlear function and to help to unravel the mechanical interaction bet ween sensory cells and supporting structures that ultimately leads to sensitive and sharply tuned auditory perception. One focus will be on the cochlea of echo-locating bats that use audition as the main window of perception to their environment and therefore have highest demands on cochlear performance.