At the 2005 World Exposition in Japan's Aichi prefecture, robots from laboratories throughout the country were on display. The humanoids came in all shapes and sizes: they moved on wheels, walked on two legs, looked like lovable little dolls or fantastic mechanical warriors. All, however, were instantly recognizable as artificial creations. Except one: it had moist lips, glossy hair and vivid eyes that blinked slowly. Seated on a stool with hands folded primly on its lap, it wore a bright pink blazer and gray slacks. For a mesmerizing few seconds from several meters away, Repliee Q1expo was virtually indistinguishable from an ordinary woman in her 30s. In fact, it was a copy of one.

To many people, Repliee is more than a humanoid robot--it is an honest-to-goodness android, so lifelike that it seems like a real person. Japan boasts the most advanced humanoid robots in the world, represented by Honda's Asimo and other bipedal machines. They are expected to eventually pitch in as the workforce shrinks amid the dwindling and aging population. But why build a robot with pigmented silicone skin, smooth gestures and even makeup? To Repliee's creator, Hiroshi Ishiguro, the answer is simple: "Android science."

Director of Osaka University's Intelligent Robotics Laboratory, Ishiguro has a high furrowed brow beneath a shock of inky hair and riveting eyes that seem on the verge of emitting laser beams. Besides the justification for making robots anthropomorphic and bipedal so they can work in human environments with architectural features such as stairs, Ishiguro believes that people respond better to very humanlike robots. Androids can thus elicit the most natural communication. "Appearance is very important to have better interpersonal relationships with a robot," says the 42-year-old Ishiguro. "Robots are information media, especially humanoid robots. Their main role in our future is to interact naturally with people."

Although Ishiguro grew up as a typical robot-model-building Japanese boy near Kyoto, he was more keen on philosophical questions about life than on inventing robots. Mild colorblindness forced him to abandon his aspirations of a career as an oil painter, and he was drawn to computer and robot vision instead. He built a guide robot for the blind as an undergraduate at the University of Yamanashi, and elements of his later humanoid Robovie went into the design of Mitsubishi Heavy Industries's new household communications robot, Wakamaru. A fan of the android character Data from the Star Trek franchise, he sees robots as the ideal vehicle to understand more about ourselves.

To emulate human looks and behavior successfully, Ishiguro yokes robotics with cognitive science. In turn, cognitive science research can use the robot as a test bed to study human perception, communication and other faculties. This novel cross-fertilization is what Ishiguro describes as android science. In a 2005 paper, he and his collaborators explained it thus: "To make the android humanlike, we must investigate human activity from the standpoint of [cognitive science, behavioral science and neuroscience], and to evaluate human activity, we need to implement processes that support it in the android."

One key strategy in Ishiguro's approach is to model robots on real people. He began research four years ago with his then four-year-old daughter, casting a rudimentary android from her body, but its few actuator mechanisms resulted in jerky, unnatural motion. With Tokyo-based robotics maker Kokoro Company, Ishiguro built Repliee also by "copying" a real person--NHK TV newscaster Ayako Fujii--with shape-memory silicone rubber and plaster molds. Polyurethane and a five-millimeter-thick silicone skin, soft and specially colored, cover a metal skeleton. Given clothing, a wig and lipstick, it is a near mirror image of Fujii.

Appearance, though, is only part of human likeness. To achieve smooth upper-body movement in Repliee, Ishiguro equipped it with 42 small, quiet air servo-actuators. Because a fridge-size external air compressor powers the actuators, locomotion was sacrificed. Similarly, Ishiguro off-loaded most of the android's control elements and sensors. Floor sensors track human movement, video cameras detect faces and gestures, and microphones pick up speech. The result is a surprisingly good. "I was developed for the purpose of research into natural human-robot communication," Repliee says in velvety prerecorded Japanese, raising its arm in instantaneous response to a touch picked up by its piezoelectric skin sensors.

Humanlike robots run the risk of compromising people's comfort zones. Says Ishiguro collaborator Takashi Minato: "Because the android's appearance is very similar to that of a human, any subtle differences in motion and responses will make it seem strange." The negative emotional reaction is known as the "uncanny valley," first described in 1970 by Japanese roboticist Masahiro Mori. Repliee, though, is so lifelike that it has overcome the creepiness factor, partly because of the natural way it moves.

One of Ishiguro's android-science experiments demonstrates the importance of movement. He had subjects identify the color of a cloth behind a curtain after it had been pulled back for two seconds. Unknown to participants, Repliee was also behind the curtain, either motionless or exhibiting prelearned "micro movements" that people unconsciously make. When the android was static, 70 percent of the subjects realized that they had seen a robot. But when Repliee moved slightly, only 30 percent realized it was an android.

In a land where Sony Aibo robot dogs are treated like family, it is not surprising that the engineering students who work on Repliee daily have developed a special protectiveness for it. Gaze-direction experiments suggest that nonengineers can unconsciously accept androids on a social level, too. In these studies, subjects pausing to consider a thought looked away during conversations with both people and Repliee, leading Ishiguro and his associates to consider that the breaking of eye contact can be a measure of an android's human likeness. They see this as key to eliminating psychological barriers to robots playing everyday roles in society. (Less sophisticated androids are already at work in Japan: Saya, a robot with fewer sensors and limited movement that was developed by Hiroshi Kobayashi of Tokyo University of Science, has been a receptionist in the university's lobby for years.)

"An android is a kind of ultimate experimental apparatus and test bed," states Ishiguro collaborator Karl MacDorman, who has been examining possible links between the uncanny valley and fear of death. "We need more of them." Although Ishiguro's automatons may even evolve to bipedalism, perhaps ironically, he is sure that androids will never be able to pass for human. There will be no need, say, for the elaborate Blade Runner-type "empathy tests." "Two seconds or 10 seconds of confusion is possible, but a whole day is not," Ishiguro remarks. "It's impossible to have the perfect android."

Still, he wants his next android, a male, to be as authentic as possible. The model? Himself. Ishiguro thinks having a robot clone could ease his busy schedule: he could dispatch it to classes and meetings and then teleconference through it. "My question has always been, Why are we living, and what is human?" he says. An Ishiguro made of circuitry and silicone might soon be answering his own questions.