Even so, Emsense, which was founded by a handful of MIT graduates, claims that its technology is superior to that which has come before it. While it hasn't published in peer-reviewed journals, it has 22 patents that cover topics that range from sensing using a dry EEG sensor to processing the data and analyzing it for its customers, says Lee. And he claims that customers, such as video-game maker THQ, creator of Frontlines, are coming back.

Emsense contacts potential testers in its database of about 5,000 people. These testers go to Emsense testing centers, scattered throughout the country, where they put on the headset and sit down to watch television or play a game. Lee explains that from the headset's data, the company's algorithms deduce a handful of coarse assessments about a tester's experience: when she has positive or negative feelings, whether or not she is concentrating, if she is excited, and, for games, how much she is engaged with it. Emsense then produces charts that qualitatively show these responses throughout the experience.

For instance, in a commercial for a detergent, an advertiser shows a pregnant woman, who is wearing a pink shirt, eating ice cream. A few seconds into the ad, she drops ice cream on her shirt, scoops it up with her spoon, and continues to eat. Toward the end of the commercial, the product is introduced, and the stain removed. According to Emsense's data, women tend to respond negatively to the first part of the ad, apparently growing distressed as the woman drops the ice cream and scoops it up. When the product name is introduced and the stain removed, women's responses turn more positive. Men, however, respond positively when the woman drops ice cream, but they remain neutral throughout the rest of the commercial. This is evidence, says Lee, that the commercial works well with its intended audience--namely, women.

But positive emotions, in particular, are difficult to measure using EEG, says Brian Knutson, professor of neuroscience at Stanford University. His group uses functional magnetic resonance imaging to peer deep within the brain, where the electrical signals that correspond positively are strong, he says. But by the time they make their way to the scalp to be measured by EEG, the signals are much weaker, and it's difficult to get a clean reading. But ultimately, Knutson says, the important question to ask is whether or not Emsense's approach is better than self-reporting, which is "a hell of a lot cheaper."