Re-visiting Al Feng’s contributions toward understanding the peripheral basis of acoustic communication in frogs

Al has made substantial contributions toward understanding the peripheral auditory mechanisms underlying acoustic communication in frogs. Al was the first to demonstrate that the basilar papilla is innervated by high-frequency auditory nerve fibers, while the amphibian papilla gives rise to low- and mid-frequency fibers. As his graduate student, we subsequently showed that the tuning of these end organs changes during post-metamorphic development. Al developed a dorsal surgical approach to the auditory nerve, which allowed the coupling between the ears to be studied. He demonstrated that both the monaural directivity patterns and the coupling between ears are frequency dependent. In a follow-up study, we manipulated the coupling between ears and concluded that the frog’s ear functions as a combination pressure/pressure gradient receiver. In this talk, I will re-visit the frequency-dependent crosstalk between the ears first described by Al in 1980. The crosstalk function is analyzed using an acoustic model of a tube with a side branch. This analysis shows the mouth cavity as the side branch is insufficient and yields a lowpass crosstalk function. Including the nares in parallel with the mouth cavity as a side branch yields a bandpass function for sound transmission that accounts for Al’s empirical crosstalk data.