Frog Studies Reveal Importance of Frequency Differences for Hearing in Noise

If you think it's difficult trying to hear what someone is saying at a cocktail or dinner party, imagine how a tree frog feels. Looking for a potential mate, they're trying to key in on a specific song in a swamp filled with a half dozen or so other frog species, each singing a slightly different tune. How do they do it?

Researchers from the University of Minnesota wanted to find out how much pitch plays a part. They simulated the call of the gray tree frog, a high-pitched series of pulses that last about a second, and embedded that call with a call simulating that of the American toad, a sequence of high-pitched tones that pulses at about the same rate but lasts a lot longer. While the female tree frog is listening for a call of 50 pulses per second, the interwoven recordings produced a call that was twice as fast, or 100 pulses per second, which she ignored. The researchers then varied the pitch, or frequency, between the frog's song and the toad's song and measured how long it took for the female to respond. If the calls were too close in frequency, the females fused them, but as the frequencies became separated, they were able to discern the tree frog song and moved toward it. The farther apart in pitch they were, the faster the females responded.

These findings are quite similar to how humans discern overlapping voices with background noise, like at a party, even though several key features of the two auditory systems-tree frogs and humans-likely evolved independently of one another. The researchers suggest that by learning how distantly related vertebrates have solved similar communication problems, we can better understand the ways that auditory systems process information encountered in a noisy environment.