Modeling sound localization using binaural cues in humpback whales

Though humpback whales have been observed accurately locating singing whales from several kilometers distance, little is known about the sound localization cues whales use. Humpback whales might use binaural cues such as differences in time of sound arrival and differences in received intensity to locate singers in azimuth. However, it is not clear that this is feasible because the differences between songs received at each of a humpback whale's ears should be quite small due to the speed of sound in water and the relatively close positioning of the whales inner ears. In this study, sound localization in whales is explored though the use of computational models. Synthesized sounds offset to represent interaural timing cues (rITDs) or filtered to represent interaural level cues (rILDs) were created from pure tones and compared using neural networks, computational models that are designed to model neuronal function. The neural networks' performances were found to accurately reflect the localization limitations of biological systems. Results revealed several potential cues for localization in azimuth. Interaural timing differences were most useful between 0.5-1.75 kHz and accuracy was greater at the midline, decreasing toward the periphery. Spectral cues also changed systematically with angle with lower boundaries between 0.15-0.75 kHz for sounds representing ILDs produced by spherical objects with a diameter of 1.0 and 0.3 m. These diameters were chosen to represent the approximate diameter of a whale's skull and the distance between a whale's inner ears respectfully. Despite the challenges of localizing sound in v/ater, cues similar to those used by terrestrial mammals appear to be available to whales.