Perception of mistuned harmonics in complex sounds by the bullfrog (Rana catesbeiana)

The ability of 73 male bullfrogs (Rana catesbeiana) to detect single mistun ed harmonics in an otherwise periodic signal was studied. Bullfrogs in thei r natural environment were presented with playbacks of synthetic signals, r esembling their species advertisement calls, that differed in the frequency of 1 harmonic component (out of 22). There were significant differences in the number and latency of the males' evoked vocal responses to these stimu li, suggesting that males were sensitive to the differences between the sou nds. Differences in envelope shape (rate and depth of amplitude modulation) produced by the harmonic mistunings may underlie the differences in respon se. Frogs, like birds and humans, can discriminate sounds on the basis of h armonic structure, indicating that this is a general perceptual bait shared among vertebrates.