@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} }