Passive echo detection and discrimination in bottlenose dolphins

Echolocation in bottlenose dolphins (Tursiops truncatus) is an active process involving outgoing signal transmission and echo reception. Transmitted echolocation “clicks” interact with a target to produce echoes that contain representative information about the target. Echolocation allows dolphins to detect, discriminate, and identify complex targets using only their hearing. However, it is unclear whether dolphins capitalize on an internal representation of echolocation clicks for matched filter processing or whether the same information (and performance) can be obtained through passive echo reception (i.e., without a corresponding ensonifying click). Here, we investigate the passive echo discrimination ability of a bottlenose dolphin by embedding a target echo in a stream of distractor echoes with similar spectral and time-domain characteristics. Initial testing has demonstrated excellent echo-discrimination ability in the light of multiple distractor echoes of similar amplitude. Additional testing is underway with expanded distractor sets and echo-ordering complexity. The paradigm specifically investigates the plausibility of perceptual identification without the potential for matched filter processing. If representational identity is attainable via a passive process and not degraded relative to active echolocation, then the function of the echolocation click might not serve in matched filter processing, though it would remain important for ensonification and in determining target location.