Virtual hands reach across the ocean

In a collaborative experiment, scientists in London and Boston showed how they can hold hands and co-operated on simple physical tasks, despite being separated by more than 3,000 miles (4,800 km)

Using force feedback devices, the participants could directly feel whether others are pulling, pushing or manipulating computer generated objects in a shared virtual world.

But long-range sensing is unlikely to arrive on home computers soon because it needs very high-speed networks to minimise delay.

Push and pull

Participants in the experiment used a computer and a small robotic arm instead of a more traditional mouse.

The robot arm developed by Sensable Technologies has on its end a device like a thick pen and is grasped by the experimenter to get a feel for what is happening in the virtual world. It also transmits their movements to other participants.

The arm, known as a Phantom, gives users the sensation of touch by exerting precisely controlled forces on the fingers.

"You can not only feel the resulting force, but you can also get a sense of the quality of the object you're feeling, whether it's soft or hard, wood-like or fleshy," said Professor Mel Slater from the computer science lab at University College London and head of one of the research teams taking part.

The other team is led by Dr Mandayam Srinivasan from the Touch Lab at the Massachusetts Institute of Technology.

Net delays

In the ground-breaking experiment, the participants shared a view of a virtual room containing a large black box. Their task was to work together to lift the black box despite being separated by the Atlantic.

One of the big problems the experimenters had to overcome was the delay caused by sending data over the net.

If there are long delays between action and reaction in the virtual world participants struggle to cope and collaborate.

Delays of less than 130 milliseconds are needed to ensure participants can work together well.

The data network used to transmit the signals across the Atlantic ran at more than 10mbps, far faster than the speeds available to home users.

"Touch is the most difficult aspect of virtual environments to simulate," said Professor Slater.

"It enhances the sense of being together even though the physical distances involved are vast."

The experiment was first carried out in May 2002 and was demonstrated in public during the Internet2 conference taking place at the University of Southern California this week.