The effects of interaural time and level differences on the binaural interaction component of the auditory brainstem response in Cope's gray treefrogs.

Processing binaural cues is crucial for many acoustic communication tasks, and understanding the neural mechanisms of binaural sound processing gives important insights into how receivers localize signalers, which in anurans is a key component of mate selection. We characterized the binaural interaction component (BIC) of the auditory brainstem response (ABR) by collecting monaural and binaural ABRs using click stimuli with varying interaural time difference (ITD) and interaural level difference (ILD) in male and female Cope's gray treefrogs (Hyla chrysoscelis). We hypothesized that the latency of the BIC peaks would increase with larger ITDs and ILDs. We also hypothesized that females would show a stronger relationship between binaural cues and BIC characteristics than males because of the greater importance of directional hearing for females. We characterized two prominent BIC peaks, DN1 and DN2. Both BIC peak latencies had a positive relationship with ITD, but there was no effect of ITD on peak amplitudes. The amplitude and latency of the BIC peaks were not affected by variation in ILD. There were no sex or body size effects on ABR or BIC characteristics. Our findings demonstrate that the BIC is driven primarily by ITD in H. chrysoscelis. This is the first study to characterize the BIC in an amphibian, which expands the comparative understanding of the neural mechanisms of binaural hearing in vertebrates.