@article {57949, title = {Mechanical basis of otoacoustic emissions in tympanal hearing organs}, year = {2014}, abstract = {

Tympanal hearing organs of insects emit dis- tortion\–product otoacoustic emissions (DPOAes), which in mammals are used as indicator for nonlinear cochlear amplification, and which are highly vulnerable to manipu- lations interfering with the animal\’s physiological state. Although in previous studies, evidence was provided for the involvement of auditory mechanoreceptors, the source of DPOAe generation and possible active mechanisms in tympanal organs remained unknown. Using laser Dop- pler vibrometry in the locust ear, we show that DPOAes mechanically emerge at the tympanum region where the auditory mechanoreceptors are attached. Those emission- coupled vibrations differed remarkably from tympanum waves evoked by external pure tones of the same frequency, in terms of wave propagation, energy distribution, and loca- tion of amplitude maxima. Selective inactivation of the auditory receptor cells by mechanical lesions did not affect the tympanum\’s response to external pure tones, but abol- ished the emission\’s displacement amplitude peak. These findings provide evidence that tympanal auditory recep- tors, comparable to the situation in mammals, comprise the required nonlinear response characteristics, which during two-tone stimulation lead to additional, highly localized deflections of the tympanum.

}, keywords = {DPOAE, Insect, laser Doppler vibrometry, locust, tympanum}, doi = {10.1007/s00359-014-0914-2}, url = {http://link.springer.com/10.1007/s00359-014-0914-2}, author = {M{\"o}ckel, Doreen and Nowotny, Manuela and K{\"o}ssl, Manfred} } @article {57948, title = {Energy localization and frequency analysis in the locust ear}, year = {2014}, abstract = {

Animal ears are exquisitely adapted to capture sound energy and perform signal analysis. Studying the ear of the locust, we show how frequency signal analysis can be performed solely by using the structural features of the tympanum. Incident sound waves generate mechanical vibrational waves that travel across the tympanum. These waves shoal in a tsunami- like fashion, resulting in energy localization that focuses vibrations onto the mechanosensory neurons in a frequency-dependent manner. Using finite element analysis, we demonstrate that two mechanical properties of the locust tympanum, distributed thickness and tension, are necessary and sufficient to generate frequency-dependent energy localization.

}, keywords = {energy localization, frequency discrimination, tension, travelling flexural wave, tympanum}, doi = {10.1098/rsif.2013.0857}, url = {https://royalsocietypublishing.org/doi/10.1098/rsif.2013.0857https://royalsocietypublishing.org/doi/pdf/10.1098/rsif.2013.0857}, author = {Malkin, Robert and McDonagh, Thomas R. and Mhatre, Natasha and Scott, Thomas S. and Daniel Robert} } @article {57946, title = {No evidence for DPOAEs in the mechanical motion of the locust tympanum}, year = {2011}, abstract = {

Distortion-product otoacoustic emissions (DPOAEs) are present in non-linear hearing organs, and for low-intensity sounds are a by-product of active processes. In vertebrate ears they are considered to be due to hair cell amplification of sound in the cochlea; however, certain animals lacking a cochlea and hair cells are also reported to be capable of DPOAEs. In the Insecta, DPOAEs have been recorded from the locust auditory organ. However, the site of generation of these DPOAEs and the physiological mechanisms causing their presence in the locust ear are not yet understood, despite there being a number of potential places in the tympanal organ that could be capable of generating DPOAEs. This study aimed to record locust tympanal membrane vibration using a laser Doppler vibrometer in order to identify a distinct place of DPOAE generation on the membrane. Two species of locust were investigated over a range of frequencies and levels of acoustic stimulus, mirroring earlier acoustic recording studies; however, the current experiments were carried out in an open acoustic system. The laser measurements did not find any evidence of mechanical motion on the tympanal membrane related to the expected DPOAE frequencies. The results of the current study therefore could not confirm the presence of DPOAEs in the locust ear through the mechanics of the tympanal membrane. Experiments were also carried out to test how membrane behaviour altered when the animals were in a state of hypoxia, as this was previously found to decrease DPOAE magnitude, suggesting a metabolic sensitivity. However, hypoxia did not have any significant effect on the membrane mechanics. The location of the mechanical generation of DPOAEs in the locust\’s ear, and
therefore the basis for the related physiological mechanisms, thus remains unknown.

}, keywords = {bioacoustics, distortion-product otoacoustic emissions, hearing, laser Doppler vibrometry, locust, tympanum}, doi = {10.1242/jeb.056465}, url = {http://jeb.biologists.org/cgi/doi/10.1242/jeb.056465https://syndication.highwire.org/content/doi/10.1242/jeb.056465}, author = {Moir, H. M. and Joseph Curt Jackson and James F.C. Windmill} } @article {57643, title = {Low-pass filters and differential tympanal tuning in a paleotropical bushcricket with an unusually low frequency call}, year = {2013}, abstract = {

Low-frequency sounds are advantageous for long-range acoustic signal transmission, but for small animals they constitute a challenge for signal detection and localization. The efficient detection of sound in insects is enhanced by mechanical resonance either in the tracheal or tympanal system before subsequent neuronal amplification. Making small structures resonant at low sound frequencies poses challenges for insects and has not been adequately studied. Similarly, detecting the direction of long-wavelength sound using interaural signal amplitude and/or phase differences is difficult for small animals. Pseudophylline bushcrickets predominantly call at high, often ultrasonic frequencies, but a few paleotropical species use lower frequencies. We investigated the mechanical frequency tuning of the tympana of one such species, Onomarchus uninotatus, a large bushcricket that produces a narrow bandwidth call at an unusually low carrier frequency of 3.2 kHz. Onomarchus uninotatus, like most bushcrickets, has two large tympanal membranes on each fore-tibia. We found that both these membranes vibrate like hinged flaps anchored at the dorsal wall and do not show higher modes of vibration in the frequency range investigated (1.5\–20 kHz). The anterior tympanal membrane acts as a low-pass filter, attenuating sounds at frequencies above 3.5 kHz, in contrast to the high-pass filter characteristic of other bushcricket tympana. Responses to higher frequencies are partitioned to the posterior tympanal membrane, which shows maximal sensitivity at several broad frequency ranges, peaking at 3.1, 7.4 and 14.4 kHz. This partitioning between the two tympanal membranes constitutes an unusual feature of peripheral auditory processing in insects. The complex tracheal shape of O. uninotatus also deviates from the known tube or horn shapes associated with simple band-pass or high-pass amplification of tracheal input to the tympana. Interestingly, while the anterior tympanal membrane shows directional sensitivity at conspecific call frequencies, the posterior tympanal membrane is not directional at conspecific frequencies and instead shows directionality at higher frequencies.

}, keywords = {auditory, katydid, laser vibrometry, Onomarchus uninotatus, Orthoptera, pseudophylline, tettigoniid, trachea, tympanum}, doi = {10.1242/jeb.078352}, url = {http://jeb.biologists.org/cgi/doi/10.1242/jeb.078352https://syndication.highwire.org/content/doi/10.1242/jeb.078352}, author = {Rajaraman, K. and Mhatre, N. and Jain, M. and Postles, M. and Rohini Balakrishnan and Daniel Robert} } @article {57637, title = {Sexual dimorphism in auditory mechanics: tympanal vibrations of Cicada orni}, year = {2008}, abstract = {

In cicadas, the tympanum is anatomically intricate and employs complex vibrations as a mechanism for auditory frequency analysis. Using microscanning laser Doppler vibrometry, the tympanal mechanics of Cicada orni can be characterized in controlled acoustical conditions. The tympanum of C. orni moves following a simple drum-like motion, rather than the travelling wave found in a previous study of Cicadatra atra. There is a clear sexual dimorphism in the tympanal mechanics. The large male tympanum is unexpectedly insensitive to the dominant frequency of its own calling song, possibly a reflection of its dual purpose as a sound emitter and receiver. The small female tympanum appears to be mechanically sensitive to the dominant frequency of the male calling song and to high-frequency sound, a capacity never suspected before in these insects. This sexual dimorphism probably results from a set of selective pressures acting in divergent directions, which are linked to the different role of the sexes in sound reception and production. These discoveries serve to indicate that there is far more to be learnt about the development of the cicada ear, its biomechanics and evolution, and the cicada\&$\#$39;s acoustic behaviour.

}, keywords = {biomechanics, hearing, high-frequency reception, laser vibrometry, predation, selective forces, tympanum}, doi = {10.1242/jeb.018804}, url = {http://jeb.biologists.org/cgi/doi/10.1242/jeb.018804https://syndication.highwire.org/content/doi/10.1242/jeb.018804}, author = {Sueur, J. and James F. C. Windmill and Robert, D.} } @article {57635, title = {The next step in cicada audition: measuring pico-mechanics in the cicada{\textquoteright}s ear}, year = {2009}, abstract = {

Female cicadas use sound when they select a mate from a chorus of singing males. The cicada has a tympanal ear; and the tympanal membrane, and constituent tympanal ridge, act as both acousto-mechanical transducers and frequency filters. The tympanal ridge is physically connected to a large number of mechanoreceptor neurons via a cuticular extension known as the tympanal apodeme. Using microscanning laser Doppler vibrometry, we measured for the first time the in vivo vibrations of the apodeme of female Cicadatra atra in response to the motion of the tympanum driven by sound. These measurements reveal that the nanoscale motion of the tympanal membrane is over a magnitude greater than that of the apodeme. Furthermore, the apodeme acts as an additional mechanical frequency filter, enhancing that of the tympanal ridge, narrowing the frequency band of vibration at the mechanoreceptor neurons to that of the male calling song. This study enhances our understanding of the mechanical link between the external ear of the cicada and its sensory cells.

}, keywords = {apodeme, biomechanics, Cicada, frequency discrimination, hearing, tympanum}, doi = {10.1242/jeb.033019}, url = {http://jeb.biologists.org/cgi/doi/10.1242/jeb.033019https://syndication.highwire.org/content/doi/10.1242/jeb.033019}, author = {James F. C. Windmill and Sueur, J. and Robert, D.} } @article {57622, title = {Tuning the drum: the mechanical basis for frequency discrimination in a Mediterranean cicada}, year = {2006}, abstract = {

Cicadas are known to use sound to find a mate. While the mechanism employed by male cicadas to generate loud calling songs has been described in detail, little information exists to explain how their ears work. Using microscanning laser Doppler vibrometry, the tympanal vibrations in the cicada Cicadatra atra are measured in response to acoustic playbacks. The topographically accurate optical measurements reveal the vibrational behaviour of the anatomically complex tympanal membrane. Notably, the tympanal ridge, a distinct structural element of the tympanum that is a link to the receptor cells, undergoes mechanical vibrations reminiscent of a travelling wave. In effect, the frequency for which the maximum deflection amplitude is observed regularly decreases from the apex to the base of the ridge. It is also shown that whilst female ears are mechanically tuned to the male\&$\#$39;s song, the male\&$\#$39;s tympanum is only partially tuned to its own song. This study establishes the presence of a peripheral auditory mechanism that can potentially process auditory frequency analysis. In view of the importance of acoustic signalling in cicadas, this unconventional tympanal mechanism may be employed in the context of species recognition and sexual selection.

}, keywords = {biomechanics, Cicada, frequency discrimination, hearing, travelling wave, tympanum}, author = {Sueur, Jerome and James F.C. Windmill and Daniel Robert} }