Auditory brainstem response in a harbor porpoise show lack of automatic gain control for simulated echoes

The auditory brainstem response (ABR) response to simulated echolocation clicks was studied in a harbor porpoise, Phocoena phocoena, to determine the relationship between the animal's perceived echo strength and the simulated target distance. In one experiment the click level at the listening post was kept constant while delay was changed, in another, the level was varied to approximate spreading losses. Results of both experiments indicate that there is no automatic gain control in the hearing system of this harbor porpoise.