Many animals communicate acoustically in large social aggregations. Among the best studied are frogs, in which males form large breeding choruses where they produce loud vocalizations to attract mates. Although chorus noise poses significant challenges to communication, it also possesses features, such as comodulation in amplitude fluctuations, that listeners may be evolutionarily adapted to exploit in order to achieve release from masking. This study investigated the extent to which the benefits of comodulation masking release (CMR) depend on overall noise level in Cope's gray treefrog (Hyla chrysoscelis). Masked signal recognition thresholds were measured in response to vocalizations in the presence of chorus-shaped noise presented at two levels. The noises were either unmodulated or modulated with an envelope that was correlated (comodulated) or uncorrelated (deviant) across the frequency spectrum. Signal-to-noise ratios (SNRs) were lower at the higher noise level, and this effect was driven by relatively lower SNRs in modulated conditions, especially the comodulated condition. These results, which confirm that frogs benefit from CMR in a level-dependent manner, are discussed in relation to previous studies of CMR in humans and animals and in light of implications of the unique amphibian inner ear for considerations of within-channel versus across-channel mechanisms.
Bibliographical noteFunding Information:
The Minnesota Department of Natural Resources and the Three Rivers Park District provided generous access to animals and study areas. Help with collecting and testing frogs was provided by J. Cook, D. Heil, J. Henderson, J. Henly, S. Hinrichs, J. Lane, A. Leightner, S. Markegaard, A. Morabu, C. Nguyen, S. Peterson, A. Rapacz-Van Neuren, K. Riemersma, D. Rittenhouse, M. Rodionova, A. Smith, K. Speirs, A. Thompson, J. Walker-Jansen, and especially S. Tekmen. This work was approved by the University of Minnesota Institutional Animal Care and Use Committee (IACUC Protocol No. 0809A46721) and was supported by grants from the National Institute on Deafness and Other Communication Disorders (Grant No. R01DC009582) and the National Science Foundation (Grant No. IOS-1452831).
This work was approved by the University of Minnesota Institutional Animal Care and Use Committee (IACUC Protocol No. 0809A46721) and was supported by grants from the National Institute on Deafness and Other Communication Disorders (Grant No. R01DC009582) and the National Science Foundation (Grant No. IOS-1452831).
© 2018 Acoustical Society of America.