Meeting Abstract

59.1  Thursday, Jan. 6  Source Segregation Based on Spectral Cues: A Mechanism for Hearing in Mixed-Species Frog Choruses? BEE, M.A.*; NITYANANDA, V.; Univ. of Minnesota, Twin Cities; Univ. of Minnesota, Twin Cities mbee@umn.edu

In humans, overlapping sounds can be perceptually separated and assigned to different sources in the environment based on differences in their acoustic properties. This capability for “source segregation” contributes to our abilities to solve the so-called “cocktail party problem” of following one conversation in multi-talker social gatherings. We tested the hypothesis that female gray treefrogs (Hyla chrysoscelis) could use spectral cues to segregate the pulsed calls of conspecific males from the overlapping, pulsatile calls of other frogs in mixed-species choruses. In phonotaxis tests, we repeatedly presented a target signal comprising a discrete pulse train (50 Hz) with a carrier frequency simulating a conspecific call. The pulses of this signal were temporally interleaved with those of a background sound comprising a continuous pulse train (50 Hz), so that the composite pulse rate was 100 Hz each time the signal was presented. Based on female selectivity for conspecific pulse rates (50 Hz), we made the following prediction. If spectral cues promote the segregation of overlapping pulsed sounds into separate sources, then females should become more responsive to the signal as a function of increasing frequency difference between the signal and background (ΔF). We tested this prediction by varying ΔF by 0, 3, 6, 9, 12, or 15 semitones across different trials. As predicted, the proportions of females responding to the signal were higher, and their response latencies lower, at larger compared to smaller ΔFs. These results confirm that female gray treefrogs were able to segregate temporally overlapping, pulsed sounds into separate sources. We suggest spectral based sound source segregation could be an important mechanism for communication in mixed-species choruses.