Kinect, an add-on to Microsoft’s Xbox 360 gaming console, is a striking advance for computer vision in the marketplace. It uses a digital camera and sensors to recognize people and gestures; it also understands voice commands. Players control the computer with waves of the hand, and then move to make their on-screen animated stand-ins — known as avatars — run, jump, swing and dance. Since Kinect was introduced in November, game reviewers have applauded, and sales are surging.