Making Waves in Hearing Research—from Whales to Humans

In the murky depths of the ocean, whales and other marine mammals sense their environment primarily though sound. Most use echolocation to navigate and find prey, and like humans, all use sound to communicate. But what exactly do they hear and how?

Darlene Ketten SM ’79 has spent decades exploring these questions, and her work has provided important insights into the correlation between ear structure and hearing in marine mammals while also contributing to the performance of cochlear implants in humans. The director of the Computerized Scanning and Imaging Facility at the Woods Hole Oceanographic Institution, Ketten has also helped debunk the theory that the sonar generated by humans is a major cause of whale deaths—though sonar can influence whale behavior.

“Animals who are underwater, in the dark, hear infinitely better than we do,” she says. But that doesn’t mean noise is necessarily problematic. The auditory experience of sea creatures is complex, Ketten explains, and different species are attracted and repelled by different sounds. “Yes, anthropogenic sounds can be a problem, but no, they won’t be a problem for every species,” she says.

In terms of whale health, she adds, “I’m more worried about pollution and ship traffic.”

MIT Opportunity

Today Ketten is among the world’s leading experts on marine mammal ears, and she made her first splash in the world of science as a graduate student at MIT.

After graduating from Washington University in St. Louis with undergraduate degrees in biology and French, Ketten studied marine biology at Florida State University. Then, she ventured to Boston and found a job as a research assistant in MIT’s Department of Earth, Atmospheric, and Planetary Sciences. “MIT was a spectacular opportunity for me, and it was accidental,” she says.

Hired to examine deep-sea specimens, she became fascinated by planktonic foraminifera and ended up pursuing her master’s degree in oceanography. Her work on foraminifera reproduction was Ketten’s first scientific paper, and it was published in Nature. After that experience, Ketten says, “I was hooked on science and research.”

Interested in studying animal behavior and communication, Ketten chose Johns Hopkins University for her doctoral work. Her plan was to study live dolphins that had recently gone on display at the aquarium in Baltimore—but something went wrong.

“I was in my first year and the dolphins started having nervous breakdowns,” she says. “It turned out the tanks were built on top of machinery that was inducing ultrasonic vibration in the tanks.”

This incident spurred Ketten to learn more about how and what marine mammals hear. Little was known at the time, so Ketten read what literature was available and examined whatever specimens she could. Her first tissue sample was a huge block of sperm whale that arrived in the mail from Iceland. That presented her with the immediate challenge of locating the ear structures within the block.

Since Johns Hopkins has a medical school, Ketten approached the imaging department for help and soon had scans made using a relatively new technology: computerized tomography (CT). “I was totally hooked on this technology,” says Ketten, whose use of CT and other scanning technologies would revolutionize the field. “These are fabulous tools to look inside at the anatomy before you started taking anything apart.”

As Ketten began scanning specimens, she noticed significant differences among species. “I thought, these are not all hearing the same frequencies the same way,” she says. For her PhD, Ketten was able to document correlations between ear structures and what frequencies could be heard by several whale species.

Work on Cochlear Implants

In 1985, Ketten returned to Boston for a postdoc in biophysics at MIT and at the Eaton-Peabody Laboratory of Auditory Physiology, Harvard Medical School. While in this role, she discovered that scientists working on cochlear implants for humans—technology that had just received FDA approval—were having trouble imaging the implants. The challenges were similar to difficulties she’d navigated while imaging the dense bones of whale ears, so she started to help the team out.

For the next 12 years, she worked to improve scanning for human patients, exploring how inner ear anatomy and pathology affect cochlear implant performance. “[That] was among the most rewarding work I’ve done because it had a direct impact on patients and the field,” Ketten says.

In 1997, Ketten joined Woods Hole to continue her efforts to understand how sound gets into the ears of marine mammals, which do not have external ear flaps to capture sound as humans do. Through imaging and examining the animals’ heads, Ketten was able to determine that special fatty tissues in the heads of whales and dolphins conduct sound into the inner ear.

Today, she is continuing to expand our understanding of marine mammal hearing by developing computer models that enable her to see how inner ear structures respond to sound. Even after decades of study, Ketten remains fascinated by the creatures of the deep. “This is the closest I’m going to get to aliens,” she says. “The oceans are an entirely different world.”