Finding a mate at a cocktail party: spatial release from masking improves acoustic mate recognition in grey treefrogs

The 'cocktail party problem' refers to the difficulty that humans have in recognizing speech in noisy social environments. Many nonhuman animals also communicate acoustically in noisy social aggregations, and thus also encounter and solve cocktail-party-like problems. Relatively few studies, however, have investigated the processes by which nonhuman animals solve sound source segregation problems in the behaviourally relevant context of acoustic communication. In humans, 'spatial release from masking' contributes to sound source segregation by improving the ability of listeners to recognize speech that is spatially separated from other sources of speech or 'speech-shaped' masking noise. Using a phonotaxis paradigm, I tested the hypothesis that spatial release from masking improves the ability of female grey treefrogs, Hyla chrysoscelis, to discriminate between conspecific and heterospecific calls that were spatially separated from two sources of 'chorus-shaped' masking noise by either 15 degrees or 90 degrees. As the signal-to-noise ratio (SNR) was decreased from +3 dB to -15 dB (by decreasing the signal level in 6-dB steps), fewer females made a choice, and the likelihood of a female choosing the heterospecific call also increased. At a SNR of -3 dB, females oriented towards and chose the conspecific call in the 90 degrees separation condition, but not when signals and maskers were separated by 15 degrees. These results support the hypothesis that a well-known solution to the cocktail party problem in humans, spatial release from masking, also plays a role in acoustic signal recognition in animals that communicate in biological equivalents of cocktail-party-like environments. (c) 2008 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.