Auditory brainstem recordings during echolocation at an aluminum cylinder in a harbor porpoise (Phocoena phocoena).

Abstract

Cetacean hearing during echolocation has only been studied in the false killer whale. A male harbor porpoise was successfully trained to perform an echolocation task while acoustic brainstem response (ABR) suction cup electrodes were attached to its body surface. The project was set up to be as similar as possible to the false killer whale studies to make results directly comparable. The porpoise was trained to position itself in a hoop 80 cm below surface. A visual screen of 1‐mm opaque plastic at 30 cm prevented the animal from using visual cues. Echolocation viewing time was controlled by an acoustical shield of neoprene foam between two aluminum plates. The shield was raised for 3 s to allow the animal free access for echolocation. An aluminum cylinder was presented at 2 m distance to the hoop 80 cm below surface in a random order 50% of the time, and the animal responded whether it detected a cylinder (GO trial) or not (NOGO trial). The ABR recordings show a clear response to the outgoing click and echoes from the target and obstacles in the near surroundings. The initial results are directly comparable to the false killer whale studies. [Work Supported by the Danish Research Council.]