Anuran amphibians are superb animal models for investigating the mechanisms underlying acoustic signal perception amid high levels of background noise generated by large social aggregations of vocalizing individuals. Yet there are not well-established methods for quantifying a number of key measures of auditory perception in frogs, in part, because frogs are notoriously difficult subjects for traditional psychoacoustic experiments based on classical or operant conditioning. A common experimental approach for studying frog hearing and acoustic communication involves behavioral phonotaxis experiments, in which patterns of movement directed toward sound sources indicate the subjects' perceptual experiences. In this study, three different phonotaxis experiments were conducted using the same target signals and noise maskers to compare different experimental methods and analytical tools for deriving estimates of signal recognition thresholds in the presence or absence of "chorus-shaped noise" (i.e., artificial noise with a spectrum similar to that of real breeding choruses). Estimates of recognition thresholds based on measures of angular orientation, response probabilities, and response latencies were quite similar in both two-choice and no-choice phonotaxis tests. These results establish important baselines for comparing different methods of estimating signal recognition thresholds in frogs tested in various masking noise conditions.
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We extend special thanks to D. Heil, J. Henderson, J. Henly, M. Kuczynski, J. Lane, A. Leightner, E. Love, K. Riemersma, D. Rittenhouse, K. Speirs, S. Tekmen, A. Thompson, A. Vélez, and J. Walker-Jansen for their assistance in collecting and testing frogs and especially to S. Tekmen for her extensive help compiling data and A. Vélez for assistance with stimulus generation. This work was conducted under Special Use Permit No. 14902 from the Minnesota Department of Natural Resources and with a Special Use Permit issued by M. Linck at the Three Rivers Park District. This research was approved by the University of Minnesota Institutional Animal Care and Use Committee (Protocol No. 0809A46721) and was funded by a Grant-in-Aid of Research from the University of Minnesota Graduate School and NIH Grant No. R03-DC008396 to M.B. and NSF Grant No. IBN-0342183 to J.S.