Background
Odontocetes inhabit three-dimensional environments where visibility is often limited. In these conditions, the use of sound and acoustic signals has been favored, leading to the evolution of echolocation.
These species produce brief acoustic pulses and analyze the returning echoes. Using the time delay between the pulse and its echo and the echo’s characteristics — such as intensity, frequency, and spectral structure — they construct an auditory representation of their surroundings
Since these animals inhabit complex environments with a lot of noise, dolphins can change the characteristics of their clicks and direct their sonar beam towards specific targets to be able to get more information and resolution on specific objects while reducing the background noise.
Studies have demonstrated that odontocetes can discriminate between targets of different sizes, shapes and material compositions. However, most of those studies have been conducted with stationary animals, which could affect on their biosonar performance.
In the wild, dolphins are highly mobile during target detection, moving their head around to change the direction of their sonar beam and and thus scan their surroundings.
Au and Pawloski (1992) studied the minimum difference in wall thickness of cylinders that dolphins were capable of distinguishing. They obtained significant results in differences up to 0.3 mm in wall thickness. However, during the experiment, the dolphin was required to be stationed in a hoop while echolocating the cylinders.
Aims
- In order to overcome the limitation of having a stationary animal, we decided to replicate the experiment but with free-swimming dolphins.
- These dolphins would be able to actively discriminate between targets as they approached them and would also be able to use their dynamic sound production and hearing abilities, along with head and body movements.