Dolphin Biosonar

We are currently investigating dolphin echolocation in collaboration with Ocean Park Hong Kong in several experiments. In general we are interested to understand how a dolphin is able to recognize the shape of an object through its echolocation sense.

Cross-modal matching

In the first experiment the dolphin is performing a cross-modal matching-to-sample task where the sample stimulus is presented to the animals echoic sense and the alternatives are presented to the visual sense – and the dolphin has to match a shape from echolocation to vision or visa versa. Stimuli are exposed to one sense only by being placed in an echoic box for echolocation exposure and in a visual display box for display to vision.

High-frequency acoustics are recorded with an array of hydrophones and synchronized to in-air and underwater video recordings. These recordings and then analyzed and processed to understand how the dolphin is able to echolocate on a complex object and recognize the shape through that sense.

Angular resolution

The second experiment investigates the dolphin’s ability to resolve two different points as separate reflections in either the horizontal or the vertical plane through echolocation. The dolphin is trained to station in a hoop underwater and to wear eyecups to ensure that the stimuli are only perceived through echolocation. For the horizontal measurement one set of two rods and one single rod is placed at a fixed distance of 2 m vertically in front of the dolphin on an arc. Then dolphin then echolocates on the rods and decides if the set of two rods is on the left or the right and indicated her choice by pressing a response paddle on either side. Throughout a test session the two sets are continuously moved closer together until the dolphin cannot discriminate between the sets anymore.

For the vertical measurement the dolphin is trained to swim into the hoop and station in it at a 90-degree rotation – then the same test procedure ensues.

Acoustic data is also collected with the hydrophone array and analyzed.

Overall both current experiments allow us to gain insight into the abilities of dolphins to recognize shapes through echolocation and might in the future allow us to develop a better sonar system based on these findings.