Cochlear microphonic potentials elicited by biosonar signals in flying bats, Pteronotus p. parnellii

Cochlear microphonic (CM) potentials were recorded from the bat, Pteronotus p. parnellii during tethered flight and during simulated flight on a pendulum. For each emitted signal the frequency of the ca. 61 kHz constant frequency (CF) component was compared with the frequency response characteristics of the animals's ear. The majority of "resting pulses' had CF components with the maximum frequency approximately 200 Hz below the best frequency (BF) of the CM audiogram. Doppler shift compensation occurred only during forward swings of the pendulum and in such a way that the echo CF components were always maintained near the BF, but on the low frequency slope of the CM audiogram. CM responses to emitted pulses were usually small in amplitude and in some animals no responses were seen. Echoes Doppler shifted upward, however, evoked high amplitude potentials. Echo CF components estimated to be at least 43 dB fainter than the emitted pulses evoked higher amplitude CM potentials than the loud emitted pulses. Echoes from large surfaces up to 4.5-5.0 meters away evoked CM potentials as high in amplitude as those elicited by emitted pulses, even when there was no Doppler shift. Beats in the CM were observed on many occasions and occurred as a result of pulse-echo and echo-echo interactions.