In that first summer Dorian began looking at the emitted echolocation signals of several dolphins. A paper had just been published that segregated false killer whale echolocation clicks into three categories and Dorian was determined to see if the application of this scheme to dolphin echolocation could be used to look for systematic variations in echolocation click production. Dorian attacked this project with enormous energy (an approach he continues to apply to his projects) and began an exhaustive study into the basics of dolphin bioacoustics and signal processing. His efforts were rewarded by his first publication in the Journal of the Acoustical Society of America (JASA) in 1999.
After obtaining his Ph.D., Dorian was awarded a National Research Council Postdoctoral Research Fellowship to continue bioacoustics research at SSC-SD and since then, Dr. Houser's contributions to the Society and to animal bioacoustics have been steady with approximately one quarter of his published works appearing in the Journal. His research has moved to the leading edge of our understanding of the effects of sound on marine mammals. Dorian developed a basis for modeling hearing in whales by using multi-threaded, evolutionary computational methods to model the hearing system of the dolphin. From that point, he ground-truthed the model's goodness-of-fit to the dolphin and applied it to the humpback whale, a species for which only anatomical data existed. For his work Dorian was acknowledged as “key personnel” in the Strategic Environmental Research and Development Program (SERDP) “Project of the Year” in 2000.
After completing his postdoctoral fellowship, Dorian formed his own company, Biomimetica, and has continued to be an integral part of the Navy's exploration into new areas of psychoacoustic measures of the hearing of marine mammals. Dorian, along with Sam Ridgway, applied medical imaging techniques to explore the physiology and anatomy of the dolphin signal generating and receiving systems. These studies marked the first time structural (MRI, CT) and functional brain scans (PET, SPECT) were performed on a living cetacean. The results had far-reaching implications, ranging from highlighting differences between post mortem and in vivo anatomy, describing in vivo the complex nasal sacs around the ears and their relationship to directional hearing, to hypothesizing on the possibility of thermoregulation of acoustic lipids in the dolphin's melon and its implications for sound transmission.
Dorian also helped develop and implement the “Biosonar Measurement Tool,” a device that captured the complete acoustic environment (signal emissions and echo reception) of a free-swimming dolphin in open-water target detection tasks. It also recorded the three-dimensional motion of the animal through the water enabling a virtual recreation of the animal's search and bioacoustic behavior. The results, published in JASA, showed how echolocating dolphins employed their biosonar during open-ocean target detection and provided insight for biologically inspired search and detection algorithms used in newly developed biomimetic sonar.
Dorian also applied his expertise in physiology to advance electrophysiological methods for hearing assessment. He is co-investigator on an effort to develop and standardize the measurement of auditory evoked potentials from marine mammals. These techniques have led to the first large scale, controlled study of marine mammal audition, with hearing tests to date being conducted on more than 42 dolphins. The results of this study revealed important relationships between animals' hearing abilities and age, gender, ancestry, and medical history and have provided key inventory management data for the Navy Marine Mammal Program.
Dorian is active in investigating potential physiological causes of marine mammal strandings. His 2001 paper in the Journal of Theoretical Biology has served as a catalyst for hypotheses explaining beaked whale strandings involving acoustically driven or activated bubble growth. Dorian is currently investigating the potential for this phenomenon by attempting to ultrasonically measure intravascular nitrogen bubbles that may form in a diving animal just after it surfaces from a series of dives. The results of this project should provide some basic answers to questions regarding nitrogen accumulation and bubble growth in diving marine mammals and lay the groundwork for understanding the potential impact of sonar on beaked whales.
In addition to possessing excellent research and experimental skills, Dr. Houser also has the important ability to maintain focus on the larger context of the research, apply the results to real-world problems, and publish work in publicly accessible, peer-reviewed literature. He has been a key participant in the development of several Navy Environmental Impact Statements assessing the potential effects of acoustic activities on marine mammals. In these technically challenging and often emotionally charged efforts, Dorian has shown tremendous skill in explaining to a lay audience complex acoustic topics ranging from acoustic metrics to the process of rectified diffusion, all while maintaining a positive and professional relationship with Navy environmental planners, government regulators, and non-governmental environmental groups.
In summary, Dr. Houser's work in marine mammal bioacoustics has made a significant impact on the state of knowledge regarding marine mammal audition and the physiological effects of sound on diving marine mammals. Dorian is active in the Society as a presenter and member of the Animal Bioacoustics Technical Committee. We believe he is an outstanding researcher with unparalleled ability and is a worthy recipient of this R. Bruce Lindsay Award.
PATRICK W. MOORE
JAMES J. FINNERAN