Gokul Rajaram, a group project manager for AdSense, said Google will take the "signals" that publishers send about their audience, which will be used to determine which ads Google sends.

Many of the signals that Google will be using are demographic, but Rajaram said that publishers also supplying other indicators, such as information they know about their visitors' other interests. "The great thing about having an active and engaged publisher community is that you can get them to define all the signals that they can think of," he said. "Even with small publishers, we've been amazed how well they know their users."

The pilot started late last month, Rajaram said, and it is too early to say when it will be rolled out to all AdSense publishers, although that is the objective. "Our goal ultimately is to scale it out and have it used by everyone," he said.

According to Jupiter Research analyst Gary Stein, this move by Google is part of the ongoing competition for publishers that has been taking place among ad networks. Yahoo! recently launched a beta version of a publisher network that also enables publishers to provide information about the types of ads that might appeal to the audience. "In general, [Google's] feeling the competition. There are a couple networks out there that are gaining some traction," he said. "Everything they're doing is giving the publishers more control, and that's really the new front in contextual advertising."

According to Stein, more control over the types of ads that are shown on their sites is a major concern for more high-profile publishers. "The larger the publisher, the bigger the consideration it is. With a marquee publisher, I think it's a high consideration," he said.