Humans and other animals often communicate acoustically in noisy social groups, in which the background noise generated by other individuals can mask signals of interest. When listening to speech in the presence of speech-like noise, humans experience a release from auditory masking when target and masker are spatially separated. We investigated spatial release from masking (SRM) in a free-field call recognition task in Cope's gray treefrog (Hyla chrysoscelis). In this species, reproduction requires that females successfully detect, recognize, and localize a conspecific male in the noisy social environment of a breeding chorus. Using no-choice phonotaxis assays, we measured females' signal recognition thresholds in response to a target signal (an advertisement call) in the presence and absence of chorus-shaped noise. Females experienced about 3 dB of masking release, compared with a co-localized condition, when the masker was displaced 90° in azimuth from the target. The magnitude of masking release was independent of the spectral composition of the target (carriers of 1.3 kHz, 2.6 kHz, or both). Our results indicate that frogs experience a modest degree of spatial unmasking when performing a call recognition task in the free-field, and suggest that variation in signal spectral content has small effects on both source identification and spatial unmasking. We discuss these results in the context of spatial unmasking in vertebrates and call recognition in frogs.
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This work was supported by NIDCD DC009582 . We thank, Alejandro Vélez for recordings of natural choruses and help generating chorus-shaped maskers, Mark Crawford, Madeleine Linck, John Moriarty, Ed Quinn, and Don Pereira for access to frog breeding sites, and Nate Buerkle, Brian Chicoine, Jenna Cook, Cally Espegard, Sarah Feingold, Noah Gordon, Nick Hein, Katie Heino, Johanna Henly, Shannon Hinrichs, Joe Kleinschmidt, Betsy Linehan-Skillings, James Mertz, Cathleen Nguyen, Steffen Peterson, Abby Rapacz-Van Neuren, Alejandro Vélez, and especially Sandra Tekmen for help collecting and testing frogs.