HOW DO OWLS LOCALIZE INTERAURALLY PHASE-AMBIGUOUS SIGNALS

Owls and other animals, including humans, use the difference in arriva l time of sounds between the ears to determine the direction of a soun d source in the horizontal plane. When an interaural time difference ( ITD) is conveyed by a narrowband signal such as a tone, human beings m ay fail to derive the direction represented by that PTD. This is becau se they cannot distinguish the true ITD contained in the signal from i ts phase equivalents that are ITD +/- nT, where T is the period of the stimulus tone and n is an integer. This uncertainty is called phase-a mbiguity, All ITD sensitive neurons in birds and mammals respond to an ITD and its phase equivalents when the ITD is contained in narrowband signals. It is not known, however, if these animals show phase-ambigu ity in the localization of narrowband signals. The present work shows that barn owls (Tyto alba) experience phase-ambiguity in the localizat ion of tones delivered by earphones. We used sound-induced head-turnin g responses to measure the sound-source directions perceived by two ow ls. In both owls, head-turning angles varied as a sinusoidal function of ITD. One owl always pointed to the direction represented by the sma ller of the two ITDs, whereas a second owl always chose the direction represented by the larger ITD (i.e., ITD-T).