Paper of the week: The cocktail party problem, how crickets solve it

Schmidt, A., & Römer, H. (2011). Solutions to the cocktail party problem in insects: selective filters, spatial release from masking and gain control in tropical crickets. PLoS ONE, 6(12), e28593. doi:10.1371/journal.pone.0028593

The ability to localize specific sounds within noisy situations is known as the ‘cocktail party problem’. One mechanism humans and animals use to improve sound discrimination is spatial release from masking – essentially, improved perception by moving away from the natural background noise or ‘masker’.

Whereas in humans this mechanism is known to benefit the perception of individual voices despite multiple speakers, it was of interest to examine the effects of spatial release in tropical crickets, whose natural habitat contains noise levels up to 60 dB. Extracellular recordings from a prominent auditory interneuron (AN1) were obtained in a laboratory setting, as well as outdoors in a tropical rainforest in Panama. Neuronal activity was amplified using a custom-made amplifier and digitized at 40 kHz with a PowerLab 4/25 for subsequent analysis.

So how do tropical crickets communicate despite a complicated acoustic backdrop? In this study three mechanisms were reported: 1. Selective frequency filtering – Maximal firing rates occurred in response to a conspecific stimulus at frequencies of 3.9 kHz, i.e. the same frequency as the male cricket’s calling song. 2. Spatial release from masking – Displacing the masker by 180° from the stimulus improved the signal to noise ratio (SNR) by 6-9 dB. 3. Gain control – A 30-60 % reduction in spiking rate in response to background noise was observed when a conspecific stimulus was introduced.

This study demonstrates that even in lower order animals sophisticated auditory processing ensures that acoustic communication can occur, despite, in some cases, profound constraints from ambient noise.

13 January 2012