Jimmy Fallon plays Project Natal (Credit: NBC)

For months now, Microsoft's leaders have been touting the concept of the natural user interface -- the ability to use gestures and voice-recognition technology to interact, via high-tech sensors, with increasingly intelligent machines. Craig Mundie, Microsoft's chief research and strategy officer, spoke at length on the topic during his recent college tour, making it clear that he considers natural user interfaces central to the future of computing.

Bill Gates raised the subject again during his appearance this weekend on "Meet the Press," telling NBC's David Gregory that the natural user interface is "the thing that people underestimate right now."

OK, so where are Microsoft's own natural user interfaces? Sure, there are prototypes, and lots of touch-screen technologies, but that's just a slice of the broader concept. Project Natal, the motion-sensing Xbox 360 control system, isn't expected to hit the market until a year from now at the earliest, despite being named one of Time's 50 Best Innovations of 2009. And Natal is still just one piece of the vision.

What's to say this won't be yet another example of Microsoft researching something to death while a rival beats it to market?

I pressed Mundie for more specifics on Microsoft's plans recently after hearing him talk to University of Washington computer-science students about the promise of natural user interfaces. Among other things, I asked if more elements of the natural user interface would show up in Windows 8, the next version of the operating system.

"Certainly the foundation for that kind of thing should be there in that time period," Mundie said, without going into specifics. "In a sense, you can say that the foundation will be there even before that, to extent that you believe that the Natal work is a precursor to these kinds of things. I'm hopeful that we'll see many of these things maturing and starting to be more generally used in that time period."

In the meantime, delivering on Natal will be one key test for Microsoft in the coming year. To be a leader this new era of natural user interfaces, the company needs Natal to live up to all the expectations generated during what has turned out to be a long hype cycle.

That means it won't be enough for Natal to let a user simply control a game with gestures, without a physical controller. More than that, the Natal technology will also need to deliver on the promise of an intelligent system that recognizes and interacts with the user, moving toward the company's broader vision.

Beyond video games, Gates told CNet News.com in July that natural controls similar to Project Natal would eventually be applied to Windows and other Microsoft programs.

Mundie also makes it clear that the motion-sensing game control system is just one example of the concept. Long term, he said, the key is to bring together machine vision, learning, hearing, and speech synthesis into an integrated system that works as an intelligent companion for the user. Many people are focusing on individual elements, he said, but the key is to pay attention to the bigger picture.

"It's the integration of these things that is the really big deal," he said.