A salient characteristic of most auditory systems is their capacity to analyse the frequency of sound. Little is known about how such analysis is performed across the diversity of auditorysystems found in animals, and especially in insects. In locusts, frequency analysis is primarilymechanical, based on vibrational waves travelling across the tympanal membrane. Differentacoustic frequencies generate travelling waves that direct vibrations to distinct tympanallocations, where distinct groups of correspondingly tuned mechanosensory neurons attach.Measuring the mechanical tympanal response, for the first time, to acoustic impulses in thetime domain, nanometre-range vibrational waves are characterized with high spatial andtemporal resolutions. Conventional Fourier analysis is also used to characterize the responsein the frequency domain. Altogether these results show that travelling waves originate from aparticular tympanal location and travel across the membrane to generate oscillations in theexact region where mechanosensory neurons attach. Notably, travelling waves areunidirectional; no strong back reflection or wave resonance could be observed across themembrane. These results constitute a key step in understanding tympanal mechanics ingeneral, and in insects in particular, but also in our knowledge of the vibrational behaviour ofanisotropic media.
- tympanal membrane
- place principle
- time-resolved laser vibrometry