Localization of sounds from a paired source in the dolphin and fur seal

Abstract

There is a notion that the dolphin’s spatial hearing operates similarly to that of humans, even though the dolphin’s ability to localize a source in the vertical plane is practically the same as in the horizontal one. Binaural phenomena are used to explain localization in the dolphin; however, there are no interaural differences in the vertical plane. Given the dolphin’s very short echolocation click and high time resolution, one would find it difficult to describe the dolphin’s hearing in terms of binaural phenomenon. The dolphin’s sonar system performs as a monaural rather than a binaural system [G. Zaslavskiy and V. Ryabov, in Marine Mammal Sensory System (1991)]. In fact, very directional sonar click transmission and reception seem to account well for the dolphin’s spatial hearing. In the present study, the way in which dolphins and fur seals respond to a sum of the signals from two sources will be discussed. There are different hearing phenomena in the human associated with the binaural perception of the sound coming from two different directions. Some of these phenomena were found in the fur seal but none of them was present in the dolphin.

Localization of brief sounds by a bottlenose dolphin

“…In humans, the echo suppression does not work for uncorrelated signals [6]. Therefore, the results appear to confirm our previous findings that the precedence effect is absent in the bottlenose dolphin auditory system [3]. Interestingly, the precedence effect appears to be absent also in bats whatever the lag sound delay [13].…”

“…The ability of a bottlenose dolphin to localize a sound in the vertical plane as accurate as in the horizontal plane appears to undermine, to a certain degree, binaural phenomenon concept in dolphin sonar [2]. The spatial hearing in the bottlenose dolphin appears to lack so-called "precedence effect" [3][4][5], which is an important attribute of binaural hearing in humans.…”