You're in your office near the end of the day, preparing to head home. You log on to your computer, navigate the desktop, open a browser, sign in to your e-mail account. You read your latest messages and write a few yourself, then log out. As you're driving home, something about the car in the next lane distracts you, but a gentle alert reminds you to pay attention to the road. When you get to your living room, you turn on your video game console. You assume an identity and traverse the virtual landscape, evading some characters, blasting others. And from the time you sit down at your desk in the office until you make your final Xbox feint, you carry out most of these interactions without using your hands or even your voice but simply by moving your eyes.

Far from being science fiction, the technology to support such a seamless merging of our digital and physical lives already exists. It is the real-world spinoff from the burgeoning field of eye tracking. Loosely defined, eye tracking refers to any technology that can monitor the direction of our gaze and the behavior of our eyes, in the process generating data that give clues to our intentions. Interactions with devices equipped with eye-tracking sensors and software can seem intuitive and effortless, as if our gadgets are reading our minds.