@article {57992, title = {Solutions to the Cocktail Party Problem in Insects: Selective Filters, Spatial Release from Masking and Gain Control in Tropical Crickets}, journal = {PLoS ONE}, volume = {6}, year = {2011}, month = {Jun-12-2011}, pages = {e28593}, abstract = {

Background

Insects often communicate by sound in mixed species choruses; like humans and many vertebrates in crowded social environments they thus have to solve cocktail-party-like problems in order to ensure successful communication with conspecifics. This is even more a problem in species-rich environments like tropical rainforests, where background noise levels of up to 60 dB SPL have been measured.

Principal Findings

Using neurophysiological methods we investigated the effect of natural background noise (masker) on signal detection thresholds in two tropical cricket species Paroecanthus podagrosus and Diatrypa sp., both in the laboratory and outdoors. We identified three \‘bottom-up\’ mechanisms which contribute to an excellent neuronal representation of conspecific signals despite the masking background. First, the sharply tuned frequency selectivity of the receiver reduces the amount of masking energy around the species-specific calling song frequency. Laboratory experiments yielded an average signal-to-noise ratio (SNR) of \−8 dB, when masker and signal were broadcast from the same side. Secondly, displacing the masker by 180\° from the signal improved SNRs by further 6 to 9 dB, a phenomenon known as spatial release from masking. Surprisingly, experiments carried out directly in the nocturnal rainforest yielded SNRs of about \−23 dB compared with those in the laboratory with the same masker, where SNRs reached only \−14.5 and \−16 dB in both species. Finally, a neuronal gain control mechanism enhances the contrast between the responses to signals and the masker, by inhibition of neuronal activity in interstimulus intervals.

Conclusions

Thus, conventional speaker playbacks in the lab apparently do not properly reconstruct the masking noise situation in a spatially realistic manner, since under real world conditions multiple sound sources are spatially distributed in space. Our results also indicate that without knowledge of the receiver properties and the spatial release mechanisms the detrimental effect of noise may be strongly overestimated.

}, doi = {10.1371/journal.pone.002859310.1371/journal.pone.0028593.g00110.1371/journal.pone.0028593.g00210.1371/journal.pone.0028593.g00310.1371/journal.pone.0028593.g00410.1371/journal.pone.0028593.g00510.1371/journal.pone.0028593.g006}, url = {https://dx.plos.org/10.1371/journal.pone.0028593}, author = {Arne K. D. Schmidt and Heiner R{\"o}mer} } @article {57423, title = {High background noise shapes selective auditory filters in a tropical cricket}, year = {2011}, abstract = {

Because of call frequency overlap and masking interference, the airborne sound channel represents a limited resource for communication in a species-rich cricket community like the tropical rainforest. Here we studied the frequency tuning of an auditory neuron mediating phonotaxis in the rainforest cricket Paroecanthus podagrosus, suffering from strong competition, in comparison with the same homologous neuron in two species of European field crickets, where such competition does not exist. As predicted, the rainforest species exhibited a more selective tuning compared with the European counterparts. The filter reduced background nocturnal noise levels by 26 dB, compared with only 16 and 10 dB in the two European species. We also quantified the performance of the sensory filter under the different filter regimes by examining the representation of the species-specific amplitude modulation of the male calling song, when embedded in background noise. Again, the filter of the rainforest cricket performed significantly better in terms of representing this important signal parameter. The neuronal representation of the calling song pattern within receivers was maintained for a wide range of signal-to-noise ratios because of the more sharply tuned sensory system and selective attention mechanisms. Finally, the rainforest cricket also showed an almost perfect match between the filter for sensitivity and the peripheral filter for directional hearing, in contrast to its European counterparts. We discuss the consequences of these adaptations for intraspecific acoustic communication and reproductive isolation between species.

}, keywords = {acoustic communication, competition, cricket, directional hearing, Matched filters}, doi = {10.1242/jeb.053819}, url = {http://jeb.biologists.org/cgi/doi/10.1242/jeb.053819https://syndication.highwire.org/content/doi/10.1242/jeb.053819}, author = {Arne K. D. Schmidt and Riede, K. and Heiner R{\"o}mer} }