Discrimination of phase spectra in complex sounds by the bullfrog (Rana catesbeiana).

1. Male bullfrogs at two different natural calling sites were presented with playbacks of synthetic advertisement calls differing in phase spectra. Sounds were presented in a ABA design to analyze the ability of the animals to perceive changes in repeated series of stimuli. 2. The number of individual croaks in an answering call significantly increased over repeated presentations of two of the three stimulus phase types in condition A1. There were significantly fewer croaks to the third stimulus. These data suggest that two stimuli were perceived in a similar manner. 3. Latency of calling to stimuli presented in conditions A and B changed in response to shifts in phase spectrum at a low density calling site. These differences were significant when comparing latency to playbacks where shifts in the phase spectrum changed the temporal fine-structure and waveform periodicity of the stimulus. 4. The increase in number of croaks and decrease in response latency across condition A1 and the increase in latency in condition B suggest that discrimination may take the form of stimulus-specific sensitization. In this context, sensitization might reflect an increase in arousal due to repeated presentation of a salient stimulus. 4. The operation of a hypothetical 'mating call detector', based on linear summation of temporal responses from the eighth nerve, provides output similar to the behavioral results.

Behavioral audiograms of the bullfrog (Rana catesbeiana) and the green tree frog (Hyla cinerea).

Reflex modification was used in a psychophysical technique to measure absolute auditory sensitivity of two species of anurans. Behavioral audiograms for these animals reveal that the bullfrog can detect sounds from 100 Hz to 3.2 kHz and the green tree frog from 100 Hz to 5 kHz. The shape and the sensitivity of these behavioral audiograms are similar to those of neural evoked-response audiograms of these animals. Absolute auditory sensitivity of anurans is only partially related to the spectral composition of their species-specific vocalizations.

Behavioral vocal response thresholds to mating calls in the bullfrog, Rana catesbeiana.

Male bullfrogs will vocalize in response to playbacks of the mating (advertisement) calls of conspecifics. This behavior was studied in response to playbacks of bullfrog mating calls presented at six different sound intensity levels. The lowest sound intensity level tested (50 dB SPL) was insufficient to evoke calling from any of the animals. Calling was evoked by playback levels of 60 dB SPL and higher. The data suggest that behavioral evoked calling thresholds lie between 50-60 dB SPL for these animals. Playback intensity levels of 80 dB SPL were more effective in evoking responses than were intensity levels up to 20 dB higher or lower. This was true both in terms of the total number of evoked responses and the trial number at which responding ceased. Moreover, significantly less habituation of evoked calling occurred at levels of 80 dB SPL than at higher or lower levels. The data suggest that a sound pressure level of 80 dB represents a behaviorally preferred intensity level for evoked calling in the bullfrog. Field recordings of bullfrog choruses show that the intensity produced by an individual calling male reaches a level of 80 dB SPL at a distance of 1 m. This intensity level is identical to that producing maximal evoked calling in the laboratory.