PT - JOURNAL ARTICLE AU - Lutz Kettler AU - Hannah Griebel AU - Roland Ferger AU - Hermann Wagner TI - Combination of interaural level and time difference in azimuthal sound localization in owls AID - 10.1523/ENEURO.0238-17.2017 DP - 2017 Dec 07 TA - eneuro PG - ENEURO.0238-17.2017 4099 - http://www.eneuro.org/content/early/2017/12/07/ENEURO.0238-17.2017.short 4100 - http://www.eneuro.org/content/early/2017/12/07/ENEURO.0238-17.2017.full AB - A function of the auditory system is to accurately determine the location of a sound source. The main cues for sound location are interaural time (ITD) and level (ILD) differences. Humans use both ITD and ILD to determine the azimuth. Thus far, the conception of sound localization in barn owls was that their facial ruff and asymmetrical ears generate a two dimensional grid of ITD for azimuth and ILD for elevation. We show that barn owls also use ILD for azimuthal sound localization when ITDs are ambiguous. For high frequency narrowband sounds, midbrain neurons can signal multiple locations, leading to the perception of an auditory illusion called a phantom source. Owls respond to such an illusory percept by orienting toward it instead of the true source. Acoustical measurements close to the ear drum reveal a small ILD component that changes with azimuth, suggesting that ITD and ILD information could be combined to eliminate the illusion. Our behavioral data confirm that perception was robust against ambiguities if ITD and ILD information was combined. Electrophysiological recordings of ILD sensitivity in the owl’s midbrain support the behavioral findings indicating that rival brain hemispheres drive the decision to orient to either true or phantom sources. Thus, the basis for disambiguation, and reliable detection of sound source azimuth, relies on similar cues across species as similar response to combinations of ILD and narrowband ITD has been observed in humans.Significance Statement Owls have evolved a high-performance sound localization system that served as a model for sound localization for >40 years, and is also used as a model for biomimetic applications. The conception so far was, that the owl uses a two-dimensional grid of interaural cues created by its facial ruff and asymmetric ears with interaural time difference for localization in azimuth and level differences in elevation. Our study extends this model by showing a major contribution of level differences to azimuthal sound localization in disambiguating unreliable timing difference information. Although auditory processing in barn owls differs from humans, our data reveals remarkable similarities in the mechanism underlying localization and cue combination across species.