DISCRIMINATION OF PHASE SPECTRA IN COMPLEX SOUNDS BY THE BULLFROG (RANA-CATESBEIANA)

1. Male bullfrogs at two different natural calling sites were presente d with playbacks of synthetic advertisement calls differing in phase s pectra. Sounds were presented in a ABA design to analyze the ability o f the animals to perceive changes in repeated series of stimuli. 2. Th e number of individual croaks in an answering call significantly incre ased over repeated presentations of two of the three stimulus phase ty pes in condition A1. There were significantly fewer croaks to the thir d stimulus. These data suggest that two stimuli were perceived in a si milar manner. 3. Latency of calling to stimuli presented in conditions A and B changed in response to shifts in phase spectrum at a low dens ity calling site. These differences were significant when comparing la tency to playbacks where shifts in the phase spectrum changed the temp oral fine-structure and waveform periodicity of the stimulus. 4. The i ncrease in number of croaks and decrease in response latency across co ndition Al and the increase in latency in condition B suggest that dis crimination may take the form of stimulus-specific sensitization. In t his context, sensitization might reflect an increase in arousal due to repeated presentation of a salient stimulus. 4. The operation of a hy pothetical 'mating call detector,' based on linear summation of tempor al responses from the eighth nerve, provides output similar to the beh avioral results.