Virtual reality has gone beyond that place in cyberspace where people can see and hear each other to now include a third sense — touch.

University researchers have made it possible for physical therapists, for example, to remotely work with patients. Now, when a patient pushes down on a rehabilitative device, a duplicate device in a remote caregiver's office responds with equal force, as if the patient were physically pressing the physician's hand. Likewise, physicians and therapists can remotely exert force on patient limbs using the system.

"This technology is important for telemedicine platforms, such as tele-rehabilitation applications," says Balakrishnan Prabhakaran, professor of computer science at the University of Texas at Dallas, principal investigator of a $2.4 million project funded by the National Science Foundation, which also includes participants from UC-Berkeley and the University of Illinois.

Prabhakaran says the system uses a technology called haptics and 3-D tele-immersion to provide a sense of touch. Haptic devices are pieces of equipment with resistance motors that apply force, vibration or motion to the user to provide feedback. The system, which is currently called 3-D TI+Touch, uses multiple 3-D cameras to create human avatars in two different places and then puts them in the same virtual space.

"3-D tele-immersion can bring people from different geographical locations into a single virtual space where those people can interact," Prabhakaran says.

Currently, in-home therapeutic prescriptive exercises are on the honor system. Patients are instructed to perform certain physical therapies, but may not be doing them correctly or doing them at all. "It's one thing for patients to say they did their exercises, but it's another to watch them, feel the force exerted and be able to correct them on the spot," Prabhakaran says.

One issue with this work has been the use of the Internet as signal carrier. Mark Spong, UT Dallas dean of engineering and computer science says implementing such a system remotely over the Internet is difficult because of the need for high fidelity signals.

"Factors such as noise and signal drops in the large amounts of data generated by the system can cause stability issues in the force reflection the system depends on," Spong says.

Spong says, however, the researchers have been able to show both in theory and experiment how to obtain good performance even when there is time delay or packet losses in transmission.