Sound source segregation in grey treefrogs: spatial release from masking by the sound of a chorus

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Abstract

Animals that communicate acoustically in noisy social environments face the problem of perceptually segregating behaviourally relevant signals from background noise. Studies of humans indicate improvements in speech perception tasks when target speech and a masking noise with the frequency spectrum of speech come from different locations. Thus for humans, spatial release from masking is an important mechanism of sound source segregation that functions in acoustic communication in noisy, real-world environments. Little previous work has investigated the mechanisms of sound source segregation in nonhuman animals that rely on acoustic signalling. I investigated spatial release from masking in the grey treefrog, Hyla chrysoscelis. Grey treefrogs form large breeding aggregations in which males produce loud advertisement calls that are necessary and sufficient for species recognition, source localization and selective mate choice by females. I tested the hypothesis that females would experience a release from masking when a synthetic advertisement call (target signal) and an artificial noise with the spectrum of a grey treefrog chorus (masker) were spatially separated. Using a phonotaxis paradigm, I assessed females' responses to the target signal at four signal-to-noise ratios (SNR) and two angular separations. Female responsiveness to the target signal increased as the SNR increased from -12 dB to +6 dB. More important, phonotaxis responses were faster at a 90° angle of signal-masker separation compared to one of just 7.5°. These results support the hypothesis that spatial release from masking is a potentially important mechanism for sound source segregation in animal acoustic communication.

Original languageEnglish (US)
Pages (from-to)549-558
Number of pages10
JournalAnimal Behaviour
Volume74
Issue number3
DOIs
StatePublished - Sep 2007

Bibliographical note

Funding Information:
I thank John Moriarty and the Ramsey County Parks Department for access to the Tamarack Nature Center, Madeleine Linck and the Three Rivers Park District for access to the Carver Park Reserve, and Ed Quinn, Mark Crawford and the Minnesota Department of Natural Resources for access to the Lake Maria State Park. Laura Cremin, Katie Grillaert, Melanie Harrington, Kasen Riemersma, Eli Swanson and Sandra Tekmen provided helpful assistance with collecting and testing frogs. Beth Pettitt, Alejandro Velez and two anonymous referees provided useful comments on earlier versions of the manuscript. This work was approved by the University of Minnesota's IACUC (No. 0510A76966) on 15 December 2005, and complied with all laws of the United States of America. Animal collections were made under Special Permit 13313 from the Minnesota Department of Natural Resources. This work was supported by a Grant-in-Aid from the Dean of the Graduate School of the University of Minnesota and NIDCD 1R03DC008396-01.

Keywords

  • Hyla chrysoscelis
  • acoustic communication
  • cocktail party problem
  • communication
  • grey treefrog
  • receiver psychology
  • sound source segregation
  • spatial release from masking
  • spatial unmasking
  • vocal communication

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