Sam Ridgway, sridgway@ucsd.edu
SPAWAR Systems Center SAN DIEGO,
Division 71500,
53560 Hull St.,
San Diego, CA 92152-5001
and
School of Medicine,
University of California, San Diego,
San Diego, CA 92093.

Lay version of paper 3aAB4
Presented 9:00 a.m. Wednesday Morning , November 12, 2008 in Room Legends 2.
156th ASA Meeting, Miami, FL

When colleagues told me that my work would be honored with special sessions at the Miami meeting of the Acoustical Society of America, I tried to think of an apt metaphor. What came to mind was the character played brilliantly by Tom Hanks in the Robert Zemeckis’ movie, Forrest Gump, based on Winston Groom’s novel. In an airy connection with Gump, in 1954, I had even received a letter from Coach Paul “Bear” Bryant inviting me to play. Unlike Forrest, I did not excel on that field. Graduating in veterinary medicine from Texas A&M University, an Air Force commission sent me to California unaware that I would soon be working with Navy dolphins. Like Gump, I flowed through the latter half of the 20 th century bumping into one challenge, then another.

In the early 1960s, I was Animal Health Officer in the beginning of the Navy Marine Mammal Program (NMMP) at Point Mugu, California. There I came to appreciate bioacoustics and psychophysics with mentors such as William Evans, C. Scott Johnson, and Ronald Schusterman. Challenged to fit dolphins to the science of the period, I worked on humane methods. Dolphins readily learned to cooperate in our experiments. They even swam freely in the open sea following our experimental protocols. Keeping the animals healthy required safe and effective anesthesia. Anesthesia was essential for some planned research. My anesthesia research enabled collaborations with pioneers in hearing and neurobiology. A dolphin pool was built at Princeton University. Surgery on the ear with James McCormick and Glenn Wever helped to elucidate dolphin sound conduction. Professor Wever’s lab at Princeton was a fertile place for discovery on all aspects of the ear and hearing. There were geckos, cats, sheep, rabbits, and reptiles and we even brought giant sea turtles to Princeton for the first study on their hearing ability. Working with McCormick at Princeton, I was able to interact with James Simmons who was doing pioneering work with bat sonar. He had a bat house at Princeton. Richard Fay had gold fish as models for understanding auditory physiology.

The famous American actor, writer, commentator, and philosopher of the 1920’s and 1930’s, Will Rogers, once said, “ The best doctor in the world is the veterinarian. He can't ask his patients what is the matter -- he's got to just know. “ I have indeed wondered if we could improve on that situation by just listening to the dolphins for a long time through hydrophones mounted in their pools with the sound piped into my lab/office. Serious people often remarked, “What is that racket!” Bioacoustician Don Carder, and Sue Moore, then a student at San Diego State University, helped me to record and analyze many 24-hour recordings of “that racket.” We have made some progress. We found that female dolphins keep relatively quiet during their period of ovulation. Perhaps a quiet female is more attractive to the male!

With Professor Theodore Bullock, at the University of California in San Diego, we recorded from some auditory areas of the dolphin brain. We found separate brain centers. One for pulse sounds used for sonar and another for whistle sounds used for social communication. Sound from the ocean travels through the dolphin’s lower jaw to the ear. The large dolphin brain is the central processing computer. The auditory parts of this computer sort out signals from the ear. From observations of dolphin capability, we adduce that they must be turning neural impulses into picture-like images. To understand these brain processes is a great challenge of dolphin neurobiology.

To forward an interest in neurobiology, I was awarded a fellowship to study at Cambridge University in England. We built seal pools atop Professor Harrisons’ Anatomy Department in Cambridge. Icelandic farmers donated gray seals for the studies. Icelandic Air flew the seals to England. We outfitted the seals with brain wave transmitters. We studied their response to sound, their control of heart function, and their sleep. Musical students in Downing College across the road learned to chorus with the seals at night. Despite neighborhood noise complaints, we finished our seal studies in 1972. However, live seals were never again allowed in Cambridge.

Back in San Diego we could make more progress with dolphins. With Professor Bullock, David Woods and Robert Galambos, we studied dolphin far field auditory brainstem responses (ABRs). These ABRs correlated with the direct brain responses we observed several years before. They might offer a way to test hearing in large whales. David Woods helped us find another very interesting brain response. Sometimes called the “ah ha” response in human studies, dolphins also showed an event-related brain potential. We thought the “ah ha” response might offer a “window on the dolphin mind.” This type of response is shown in the third picture below.

Another potential “window” appears with the use of modern scanning technology. With the help of collaborators, especially Dorian Houser, we use positron emission tomography (PET). PET gives us a map of brain activity in response to different sounds. One such map is shown in the second picture below.

Because hearing is crucial for their echolocation and communication, the problem of deafness is a special concern for dolphins. Our colleague, Darlene Ketten at Woods Hole has been examining marine mammal ears to pin down the anatomical signs of hearing loss and deafness. Don Carder and I found a dolphin that was deaf and mute. We also found several older animals, mainly old males that had lost high-frequency hearing. Severe infections such as meningitis can cause deafness even before birth. Parasites, especially flukes, and certain medications can cause hearing loss.

Deafness or high-frequency hearing loss can result from exposure to loud sound. In recent years, concerns have arisen about human-generated sound in the ocean – especially high-powered sonar. A National Research Council committee was convened to assess this issue. Colleagues on these committees, especially Dennis McFadden, urged collection of marine mammal data on temporary threshold shift (TTS). With my associates Don Carder and Carolyn Schlundt we set out to collect such data to establish acoustic safety criteria. We reasoned that animals exposed to sound levels at or below the TTS level could not be injured by sound. Soon we were joined by James Finneran who has greatly expanded this work.

At the NMMP, we are concerned with dolphin audiometry and in improving diagnostic methods for hearing assessment. My colleague James Finneran developed a portable system for rapidly tests of hearing in marine mammals. The system called EVREST is based on a laptop computer. The computer runs software that Dr. Finneran developed. A trained operator with this system can rapidly to do audiograms at distant marine parks or on beaches where whales or dolphins have stranded.

The fictional Forrest Gump often happened to be ‘there’ for momentous events in the last half of the 20 th century. In my smaller world of dolphin science, events have often worked a little like that. For example, I happened to attend a meeting in Hawaii with several experts on cetacean sonar and hearing. ‘There’ on Oahu with Bertel Mohl, Whitlow Au, Paul Nachtigall and Alexander Supin when a baby sperm whale stranded on Maui for testing again illustrated the Gump Effect: "Life was like a box of chocolates. You never know what you're gonna get."