Temporal information processing in gray treefrogs: Compute within frequency then integrate across frequency

Abstract

In Cope’s gray treefrog (Hyla chrysoscelis), the pulse rate of advertisement calls is a species recognition cue. This temporal information is redundant across two spectral bands in the call’s bimodal spectrum that are primarily transduced by different inner ear papillae. Previous studies have shown that some neurons in the frog auditory midbrain are selective for bimodal spectra and that, compared with unimodal spectra, calls with bimodal spectra are more attractive. In addition, “interval-counting” neurons in the frog auditory midbrain are selective for conspecific pulse rates. However, it is not known whether pulse rate information is computed prior to, or subsequent to, spectral integration. We conducted behavioral experiments to investigate the serial order of pulse rate computations and spectral integration. In phonotaxis tests that used bimodal and unimodal stimuli with variable pulse rates, we tested the hypothesis that spectral information is integrated prior to pulse rate computations versus the alternative hypothesis that pulse rate can be computed independently in different frequency channels prior to spectral integration. Our results support the latter hypothesis, and suggest pulse rate can be computed independently in separate frequency channels. These results give insight into the mechanisms of temporal processing underlying the perception of key biological information.