Sunday, 11 June 2017

Cope's gray treefrogs meet the cocktail party problem

With hundreds of males calling at the same time, how's a female to choose a mate? Like this.

Date: June 7, 2017
Source: University of Minnesota

You've been there: Trying to carry on a conversation in a room so noisy that the background chatter threatens to drown out the words you hear. Yet somehow your auditory system is able to home in on the message being conveyed by the person you're talking with. The secret to rising above the noise -- a dilemma known in the world of sound science as "the cocktail party problem" -- turns out to lie in its ability to discern patterns in the background noise and selectively ignore such patterns, according to a new study published in Current Biology earlier this month.

Frogs mating
Listening to a deafening chorus of Cope's gray treefrogs on a spring evening, scientists have wondered: Do female frogs use a similar strategy to pick important messages about potential mates out of the cacophony? The chorus consists of the calls of countless individual male frogs, each of which is conveying information about which species it is and how fit it is -- with faster, longer calls indicating fitter individuals. To ensure the best survival of their young, "the females have to be able to tell the appropriate species and be able to choose a high-quality male," says Norman Lee, a postdoctoral fellow in the Department of Ecology, Evolution, and Behavior. But how can they, when everyone is talking at the same time?

Working with associate professor Mark Bee and colleagues in EEB and the Department of Psychology, Lee has figured out what traits of the background noise of frog choruses allow females to tune out the hubbub and tune into the hubba-hubba -- with implications not only for our understanding of frog ecology and evolution, but also for our ability to help humans hear.

Lee knew from others' research that humans are able to hear certain sounds better in noisy settings when the background noise is "comodulated" -- meaning that the various frequencies of sound it comprises vary in loudness together. Could the fact that the background noise is comodulated be a key to the frogs' success? To find out, he first built a model of the Cope's gray treefrog's ear and used it to determine how this species may process the background chorus. He then analyzed frog choruses and discovered that the chorus input indeed is comodulated.

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