Acoustic Touch Screen for Dolphins
J. Starkhammar, M. Amundin, H. Ols鮬 M. Ahlmqvist, K. Lindstr?H. W. Persson
Dolphin sonar has been extensively studied over several decades, and much of its basic characteristics are well known (Au 1993). However, most of these studies have been based on an experimental setup where the dolphin has been trained to be voluntarily fixed, so its directional sonar beam could be recorded with fixed hydrophones. Although this allows for very exact measurements, it most likely has prevented the full dynamic potential of the dolphin’s sonar to be revealed. Also the dolphin’s response to scientific questions, e.g. in target detection threshold or discrimination trials, mostly has been a “go/no go” response or pressing a yes/no paddle. This traditional experimental methodology to measure the response makes rather coarse indications of choice. It is difficult to refine and will be unpractical with a multi-choice paradigm.
Therefore a new EchoLocation Visualisation and Interface System (ELVIS) has been developed at Lund University in cooperation with Kolmården Wild Animal Park, and is presently being used in dolphin food preference investigations at the Kolmården Dolphinarium. ELVIS basically consists of a matrix of 16 hydrophones attached to a semi transparent screen lowered into the water of the pool where the dolphins swim freely. The hydrophones hit by a sonar pulse generate electric signals in relation to the received sound pressure level. After subsequent amplification these signals are transferred to a computer. The signal analysis is performed by custom designed LabVIEW software that constitutes the core of the interactive features of the interface system. The software can for example in real time create a round colour spot on the computer screen, corresponding to the maximum intensity in the sound beam. The recorded sound intensity can be coded into colour and/or light intensity. The resulting image on the computer screen is continuously projected back onto the hydrophone matrix screen, hence giving the dolphin an immediate visual feedback to its sonar output. Since only 16 hydrophones were used, the exact location of the maximum sound intensity point was derived through interpolation between the hydrophones in the matrix. This made the spatial resolution of the sound beam recordings quite sufficient for the present study. However, future systems will certainly rely on increased hydrophone matrix size. This system offers a whole new experimental methodology in dolphin research since it can function as an acoustic “touch screen” for the dolphins. It is highly adaptable to different studies since the core of the interface features is software based.
In cognitive studies with primates, e.g. the chimpanzee, a computerized symbol interface, based on a finger operated touch screen, has been successfully used (Rumbaugh et al. 1975). Even with birds, like chickens and doves, this approach has been used (Cheng & Spetch, 1995). So far, however, it has not been attempted with dolphins, partly due to the inherent problems in using electronics in salt water. However, the ELVIS screen is based on acoustic detection and activation, using hydrophones, which is well suited for underwater use. The software used in the present experiment designate active areas on the screen, indicated by white symbols, e.g. a filled circle or a filled square. When the dolphin aims its sonar beam axis at this symbol, it flashes to indicate a “hit” and a bridging stimulus (a 400 ms, 10 kHz sinus tone) is played. In this study each of four such symbols represented a different fish (herring, mackerel, capelin and squid). When the dolphin “clicked” on one of them, it was rewarded by the fish represented by it. Thereby the dolphin could choose what kind of fish it preferred. Hence, for the first time the dolphins could execute and run a computer program using their sonar beam like we use a mouse cursor. The size and trig level of these “buttons” or active areas of the screen can easily be altered so that, as the dolphin’s skills in handling the program increased, the more accurate hits and more distinct sound pressure levels of the dolphin’s sound beam could be required.
Three bottlenose dolphins (Tursiops truncatus) were trained to perform the task of pointing their sonar beam selectively on the symbols shown on the ELVIS screen. They quickly learned this task and were highly motivated to explore it.
Ain't it great??? 
