BALTIMORE – One minute, Anne Mekalian's brain is telling her prosthetic arm to unstack a set of multicolored plastic cones, and the shiny black metal limb is listening. Every now and then, the plastic clatters to the table, but quickly the cones are separated and restored to a neat pile. The next moment, though, the bionic hand doesn't know what to make of slight muscle movements in Mekalian's forearm, interpreted through a set of electrodes touching the skin on the rounded remnant limb that extends just below her elbow. Instead of pinching a red clothespin, the robotic hand spins like Linda Blair's head in "The Exorcist."

"This is why it's experimental, right?" Mekalian, of Joppatowne, Md., joked scientists who had gathered in an office at Johns Hopkins Hospital to watch her as part of clinical trials of advanced prosthetics.

The technology is advancing quickly. Over the past several months, Mekalian and two other amputees working with a Johns Hopkins Hospital surgeon and local company have been among the first in the nation to take home thought-controlled robotic arms designed for wounded veterans.

While the devices haven't been perfect replacements for limbs lost, they have brought a glimpse of what patients took for granted before being struck by infection, cancer or violence.

Trial and error applying the technology to their daily lives — putting on makeup, cooking, carrying a laundry basket — is leading to refinements.

The scientists say the technology could be available within a couple of years to countless others commercially, with plans for U.S. Food and Drug Administration review next year.

Scientists say the technology could be available commercially within a couple of years.

Before that can happen, the scientists are learning all they can through the 67-year-old Mekalian and the others. "We're almost inventing a new field of medicine," said Dr. Albert Chi, a Johns Hopkins trauma surgeon working with the patients. "We're kind of learning as we go. There's no textbooks out there."

For the past two years, Chi has worked with Baltimore's Infinite Biomedical Technologies and Advanced Arm Dynamics, a Texas-based developer of prosthetics, to blaze the trail, starting with Johnny Matheny, a West Virginian who lost his left arm to cancer in 2008. Dana Burke, a Pennsylvania woman who lost her right arm about 5 inches below her shoulder after a shooting 15 years ago, came next.

Efforts to develop the device began in 2006, under a program of the U.S. military's Defense Advanced Research Projects Agency. The Johns Hopkins Applied Physics Laboratory, hired for $35 million in 2010, was responsible for developing the technology for soldiers returning from the wars in Iraq and Afghanistan with amputations.

Now Mekalian has joined Matheny and Burke in various successes and frustrations as they serve as guinea pigs.

Just two years ago, it wasn't a position the third-grade teacher expected to be in. But then her health took a sudden, disastrous turn. A strep infection caused pneumonia in both of Mekalian's lungs and put her body into sepsis. Her extremities began to blacken with gangrene. She had to undergo quadruple amputation, below the knees and elbows.

As she began rehabilitation, she read a Baltimore Sun article about Burke and saw a "60 Minutes" piece featuring Matheny, who were both working with Chi. She wondered if she might be able to use the technology, too.

Within days of a call to the Hopkins physics laboratory, she was connected with Chi.

The high-tech prosthetics are the closest thing to a flesh-and-bone arm and yet are no more invasive than traditional "body-powered" devices. With those prosthetics, amputees might activate a pincer hand by using their opposite shoulder to pull a cable within the device.

But to control Mekalian's prosthetic arm, down to each robotic finger, she does little more than think — just as she did before her amputation.