LAUSANNE, Switzerland — Swiss scientists have demonstrated how a partially paralyzed person can control a robot by thought alone, a step they hope will one day allow immobile people to interact with their surroundings through so-called avatars.

On Tuesday, a team at Switzerland's Federal Institute of Technology in Lausanne used only a simple head cap to record the brain signals of Mark-Andre Duc, who was at a hospital in the southern Swiss town of Sion 62 miles away.

Duc's thoughts — or rather, the electrical signals emitted by his brain when he imagined lifting his paralyzed fingers — were decoded almost instantly by a laptop at the hospital. The resulting instructions — left or right — were then transmitted to a foot-tall robot scooting around the Lausanne lab.

Rajesh Rao, an associate professor at the University of Washington, who has tested similar systems with able-bodied subjects, said the Lausanne team's research appeared to mark an advance in the field.

"Especially if the system can be used by the paraplegic person outside the laboratory," he said in an email.

Duc lost control of his legs and fingers in a fall and is partially quadriplegic. He said controlling the robot wasn't hard on a good day. "But when I'm in pain it becomes more difficult," he said.

Background noise caused by pain or even a wandering mind has emerged as a major challenge in the research of so-called brain-computer interfaces since they first began to be tested on humans more than a decade ago, said Jose Millan, who led the Swiss team.

To get around this problem, his team programmed the computer that decodes the signal so that it works in a similar way to the brain's subconscious. Once a command such as 'walk forward' has been sent, the computer will execute it until it receives a command to stop or the robot encounters an obstacle.