Adaptation of the peripheral auditory system of CF-FM bats for reception and analysis of predominant components in orientation sounds and echoes

Abstract

In Rhinolophus ferrumequinum and Pteronotus parnellii, each orientation sound consists of long constant-frequency (CF) and short frequency-modulated components. The CF component, which is predominant in the orientation signal, is about 83 kHz in R.f. and 61 kHz in P.p.r. The peripheral auditory system of these bats in terms of CM and N1 is so sharply tuned to the sound at either 83 or 61 kHz, that signal-to-noise ratios significantly increase at these frequencies. The excitatory tuning curves of primary auditory neurons tuned at either 81–86 kHz (R.f.) or 60–63 kHz (P.p.r.) are very narrow. The Q10 dB values, 100 on the average, can be as high as 400. These neurons can code a very minor frequency shift such as ±0.012%. The peripheral auditory system is thus specialized for the reception and free frequency analysis of the predominant component of orientation sounds and echoes. This specialization is not due to suppression or inhibition, but due to the mechanical specialization of the cochlea. [Work supported by NSF.]