Improvement of directionality and sound-localization by internal ear coupling in barn owls

Mark Konishi was one of the first to quantify sound-localization capabilities in barn owls. He showed that frequencies between 3 and 10 kHz underlie precise sound localization in these birds, and that they derive spatial information from processing interaural time and interaural level differences. However, despite intensive research during the last 40 years it is still unclear whether and how internal ear coupling contributes to sound localization in the barn owl. Here we investigated ear directionality in anesthetized birds with the help of laser vibrometry. Care was taken that anesthesia and the stapedius reflex did not influence the results. When analyzed in narrow frequency bands, the data demonstrated a certain amount of internal ear coupling in the low-frequnecy range (<3 kHz), but not in the high frequency range (3-10 kHz). Although many cells in the auditory pathway are tuned to interaural time difference in the low-frequency range, barn owls hesitate to approach prey or turn their heads when only low-frequency auditory information is present in a stimulus they receive. Thus, the barn-owl's sound localization system seems to be adapted to work best in frequency ranges where interaural time and level differences may be simultaneously evaluated for localizing prey.