Solutions to cocktail-party-like problems in acoustic insects

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. This is a particular problem in species-rich environments like tropical rainforests with background noise levels of up to 60 dB SPL. I describe three “bottom-up” mechanisms in cricket receivers, which contribute to an excellent neuronal representation of conspecific signals under such conditions. First, more sharply tuned frequency selectivity of the receiver reduces the amount of masking energy around the species-specific calling song frequency, resulting in a signal-to-noise ratio (SNR) of −8 dB, when masker and signal were broadcast from the same side. Second, spatial release from masking improved the SNR by further 6 to 9 dB. Neurophysiological experiments carried out in the nocturnal rainforest yielded a further improvement of SNRs by 8 dB compared to the laboratory. Finally, a neuronal gain control mechanism enhances the contrast between the responses to signals and the masker, by inhibition of neuronal activity in inter-stimulus intervals. The results indicate that without knowledge of receiver properties and the spatial release mechanisms the detrimental effect of noise may be strongly overestimated.