Department Seminar of Zahi Cohen - Invariant Echo-Localization Using Bat Pinnae (External Ear)

Sound localization is arguably one of the most important functions of the vertebrate auditory system. Animals must properly localize the sound of a predator, a prey or a potential mate. The mammalian external ear (the pinnae) has evolved especially to assist sound localization. The pinnae is thought to generate spectral cues that enable assigning a specific sound spectrum to a specific direction in space. Echolocating bats must constantly localize the direction of acoustic targets – the echoes reflected from different objects. Bats have a uniquely difficult task because echoes are naturally filtered (due to target shape and distance) independently of target direction. To examine if and how the bat pinna allows solving this ambiguity, we used a bio-mimetic system which included a 3D model of the bat pinna and which allowed us to emit bat-like echolocation signals and record the echoes. In our study, we focused on echolocating bats and showed how crucial external ears are for echo-localization. The setup model that included pinnae performed far better than the no-pinnae model allowing accurate sound localization independently of object shape and distance. The pinnae also improved the uniformity of the performance – allowing better sound localization for any azimuth angle. Using a simple computational and physical model, we managed to quantify the advantage of evolving external ears. Unlike most previous studies, we generated actual echoes from various shapes and estimated our ability to localize them based on the reflected spectra, comparing a setup that included a 3D model of the external ear to one that did not. We developed a mathematical framework to estimate the azimuth of the sound source based on its spectrum, and we specifically examine how pinnae affect localization accuracy for targets of different shapes and at different distances.