Underwater ears. A mechanical engineering doctoral student and researcher at the Woods Hole Oceanographic Institution, Jason Holmes (ENG’03,’06), recently developed a low-cost, highly sensitive underwater listening device that could prove useful to oceanographers as well as the U.S. military.

Comprised of six underwater microphones, or hydrophones, placed inside a 30-foot plastic tube filled with mineral oil, the acoustic sensor is towed behind a small, unpiloted submarine. With the mineral oil creating neutral buoyancy — ensuring that the tube neither sinks nor rises to the ocean surface — the device stores data on mini-disc recorders aboard the submarine. Called Remus, the sub was designed at Woods Hole.

Holmes and his advisor, William Carey, an ENG professor of aerospace and mechanical engineering, say the device could help scientists understand properties of ocean sediments and the seabed, as well as help the military detect oceangoing threats to America’s waterways. Holmes presented the research, which is supported by the U.S. Navy, at a meeting of the Acoustical Society of America in Vancouver on May 20.

A primary innovation of their listening apparatus is its compact size. Similar equipment used by ocean scientists and the military typically are towed behind ships and are very long, the shortest being about 1,500 feet in length and several inches in diameter. In contrast, Holmes’ prototype, 30 feet long and 1.1 inches in diameter, is pulled easily by a small, quiet battery-powered craft. (The compact, torpedo-shaped Remus can navigate around obstacles and through harbors using GPS sensors, sonar, and electronic maps.)

Parts for Holmes’ array cost a mere ,000 and are available as off-the-shelf technology, making his invention vastly more cost-effective than the multimillion dollar listening arrays currently used by the military as security tools.

“A lot of people were skeptical this would even work,” says Carey. “But the way Jason has designed this array . . . will change the way ocean measurements are made.”

Holmes is now working with the military to further develop the array for underwater intelligence-gathering. His next project will comprise four underwater hydrophone arrays towed by a fleet of unpiloted subs that could travel up to four kilometers per trip. Holmes and Carey say they envision a fleet of entirely autonomous listening subs that will prowl the seas, returning to underwater recharging stations to upload their data and refresh their batteries.

Secrets of subliminal messaging. Most people have heard of subliminal messages — words or images that are designed to influence a person without his or her awareness — but the mechanism that makes them work has long been considered a mystery. Now, a team of researchers at Boston University’s Center for Memory and Brain, led by Takeo Watanabe, a CAS associate professor of psychology, has identified the way subliminal learning works in the brain.

Subliminal learning takes place when people are unknowingly influenced by some kind of stimulus, such as words spoken slightly below hearing level or images displayed faster than the eyes can process them. To determine how this process works, Watanabe and his team created several perception tests in which participants were asked to pay attention to a series of flashing letters and identify letters of a certain color. As the letters flash on a computer screen, a series of moving dots appears slightly below the line of vision. Participants were tested on the length of time it took each person to identify the direction and movement of the dots. The recognition time improved in subsequent tests, demonstrating both that participants were able to learn subliminally, identifying the dots even while focusing on the letters, and that they were able to retain the information between tests.

The latter finding, Watanabe says, may indicate that the visual cortex of the brain, long thought to be unchangeable past infancy, remains impressionable well into adulthood. The participants were tested six months after the initial trials, and showed little loss of the information they had learned.

“It’s possible that other parts of the brain could work this way too,” Watanabe says. “People might be able to improve their pronunciation of a new language if it’s presented simply, without paying attention. It’s possible the brain could be changed without a lot of effort.”

Watanabe’s group plans to repeat the experiments using functional magnetic resonance imaging, or fMRI, to peer into the brains of participants. Using fMRI, the team will essentially be able to look directly into the portion of the brain involved in subliminal learning. The team’s initial findings were presented at the American Psychological Society meeting in Los Angeles at the end of May.