The product demonstration room at Immersion Medical in Gaithersburg, MD, is a veritable arcade of medical simulation. There you can find a lineup of electromechanical, sensor-riddled, computerized devices, all coupled to virtual models of the human body. With these gadgets, students can practice the routine task of inserting a catheter into a patient's hand, or more difficult procedures like a colonoscopy or even a lung biopsy. But these simulators don't just provide vivid computerized visual renderings of human innards. They also re-create something equally critical: how all the injecting, cutting, inserting and palpating actually feel to the doctor performing them.

Here and in other corporate and university labs, computer simulation experts-having largely mastered visual displays and digitized sound-are demonstrating an increasing mastery over a third sensory frontier: touch. Their specialty is known as haptics, after the Greek haptikos, meaning to grasp or perceive. While the technology is still most widely known as the rudimentary shuddering of a video game joystick, more sophisticated versions are well on their way to enhancing basic medical simulation training.

Future haptic applications may even enable doctors to perform surgery over the Internet. Beyond medicine, haptics has also emerged as a tool for creating "touchable" 3-D models in the virtual world, and for conveying bumps and vibrations on the common computer mouse-you'd "feel" the icons on the screen (see companion article "Touchy Subjects"). But the technology is having its most palpable impact as an emerging tool for training doctors and nurses without risk to patients. "Haptics is a huge part of providing a realistic [medical] simulation experience," says Gregory Merril, Immersion's 32-year-old founder and self-described chief visionary officer. "When doctors are interacting with patients, a lot of it is the sense of touch."

The net result of this amalgamation of hardware, software and mechanisms was that the procedure felt intuitively right: easy through the skin, resistance as the needle popped through the blood vessel wall, and a feeling of release as the needle reached the bloodstream. Even my ears were engaged, as my maiden foray into catheterization elicited jarring "ouches" from the computer's speakers: cries of pain from the violated virtual man.

But, hey, I'd done it. Feeling good, I decided to take a stab at something more challenging: pediatrics. But after my third try at easing a thin-gauge catheter into a vein on a newborn baby's virtual forehead, I gave up. My angle was too low. The resistance in the needle told me as much. The virtual baby told me, too, as shrieks rattled the speakers. Maybe I wasn't meant to be a doctor after all.

Merril characterizes the hardware components of his company's simulators as novel uses for existing mechanical and robotic components. With combinations of electromagnetic brakes, motors, cables and other devices, he says it's possible to convey a wide range of tactile sensations. What makes it seem "like you are really sticking the needle in...and that you are feeling a force that corresponds to what you are seeing, is a computer model of the skin," Merril says.