Spectral Peak Onset and Offset in H. Cinerea
Many animals face a "cocktail party problem" in which they must recognize acoustic signals in a noisy social environment. Given that current hearing aid and voice recognition technology functions poorly in such environments, it is crucial to determine how such signals can be sorted out. The green treefrog, Hyla cinerea, has evolved to large breeding choruses, providing a model to study how this process is undertaken. Males produce mating calls with two distinct spectral peaks which help facilitate call recognition. It is known that synchronous onsets of these peaks aid in their perception as a unified call. However, there is a gap in knowledge pertaining to the extent of onset and offset asynchrony in natural male calls. The central hypothesis of this study was that auditory systems evolved to exploit regularities in acoustic mixtures, arising from the physics of sound production. The working hypothesis was that treefrog calls are structured so that onset synchrony can be used as a cue to sort out acoustic mixtures in a chorus. I determined the onset and offset asynchrony between spectral peaks in 437 calls from 22 wild H. cinerea males. The duration of onset asynchrony was significantly lower than that of offset asynchrony. Additionally, both onset and offset asynchrony duration were lower than the value necessary for females to perceive a call. These results suggest that H. cinerea calls have evolved to fine tune onset synchrony, and that shorter onset asynchrony may necessitate shorter offset asynchrony in terms of physically producing acoustic signals.