As if television-watching isn't getting complicated enough, now advertisers want to find out if you have been paying attention.

With the number of viewers for individual networks continuing to dwindle, other ways of measuring audiences have emerged, from age to wealth to gender. Now executives increasingly are talking about "attentiveness" -- how engaged a person is in a particular program, and therefore how aware they are likely to be of the commercials and product placements that appear during one. The goal: to reach viewers who recall advertised products rather than those who are inattentive couch potatoes.

When people watch NBC's medical sitcom "Scrubs," for instance, they pay more attention than when they watch "60 Minutes" on CBS, according to a new kind of research. If such a metric becomes an accepted way of evaluating audiences, it could transform the way advertisers buy TV time.

Monday, the broadcast networks will begin the time-honored process known as the "upfront," when they tout their coming fall prime-time schedules to Madison Avenue. The air will be rife with calls from advertisers to develop better ways to derive tangible and measurable results from their advertising.

In recent days, three big TV companies -- General Electric Co.'s NBC Universal, Viacom Inc.'s CBS and News Corp.'s Fox -- have signed contracts with IAG Research, a New York firm that measures audience reaction to, and recall of, TV commercials and product placements. IAG is discussing a similar deal with Walt Disney Co.'s ABC and Time Warner Inc.'s WB network, representatives of both companies confirm. Also using IAG's services are advertisers that include Toyota Motor Corp.'s Toyota Motor Sales USA, General Motors Corp. and News Corp.'s 20th Century Fox studio.

In the meantime, traditional measurements, such as how many people are watching, are becoming somewhat more slippery. The rise of new technology -- video on demand and personal-video recording devices that encourage ad-skipping -- is making it much easier for people to view programs when they want, not as a network schedule demands.

IAG measures viewer response to shows, ads, product placements and on-air promotions, surveying 900,000 people via the Internet. Each panelist is tapped three times a week to answer questions about three programs. IAG's research shows that for the week ending May 1, programs such as NBC's "Scrubs," ABC's "Desperate Housewives," Fox's "Family Guy" and UPN's "Veronica Mars" earned some of the highest show-attentiveness scores among network prime-time programs among viewers 18 to 49. Among the lowest: news programs such as "60 Minutes" and NBC's "Dateline NBC." David Poltrack, executive vice president of research and planning for CBS Television, points out that viewers aged 18 to 49 are not the primary watchers of newsmagazines, which tend to have more "in and out" viewing than scripted dramas. VNU's Nielsen Media Research says "Desperate Housewives," Fox's "American Idol" and CBS's "Survivor: Palau" and "Crime Scene Investigation" were among the top-rated programs for the week.

IAG measures, among other things, a viewer's recall of a commercial or a product placement in a show, and his or her opinion of those two. Participants answer the survey based on shows and commericals they have already watched.

The new data will "move us beyond the age and sex numbers that we usually use" and measure "impact as opposed to just exposure," says Jon Nesvig, president of ad sales for Fox Broadcasting Co.

For years, TV executives have noticed in the rerun business that certain shows demanded more attention. Huge syndicated hits such as "Wheel of Fortune" and certain less taxing sitcoms were perfect for the late afternoon and early-evening time periods because viewers could cook dinner and do chores and still get what was going on. Complicated dramas such as "NYPD Blue" work in reruns late at night, if at all. This is conventional wisdom, but no one ever talked much about the implications for advertisers.

"You're going to want to know more and more how a viewer perceived that show -- is it important to them? If it is important to them, are the commercial messages more important to them than in a show that they are not all that excited about?" asks WB Chairman Garth Ancier.

Broadcasters already are using some of these studies to tout themselves over their cable rivals, saying that cable viewers are "roamers and surfers" and their shows are more carefully watched. Certain cable channels, of course, undoubtedly could take the same research and use it to promote their offerings.

Network executives also hope to use the new research to value the product-placement deals that are increasingly sought by advertisers. Product placement -- embedding a certain product within a show -- is now negotiated in willy-nilly fashion, with a number of different parties involved and no set rules to follow. Moving to a system with clear criteria would be helpful, says Alan Wurtzel, president of research and media development for NBC Universal.

IAG's data is "useful" says Lisa Quan, a vice president and manager of broadcast research at Interpublic Group of Cos.' Magna Global, a media-buying and research firm, "but I don't think you can say that it is totally representative of your normal television viewers and their habits." One concern: IAG's panel is based on Internet users, but not all TV viewers have computers or Internet access. IAG's methodology, says co-Chief Executive Alan Gould, is "sound, tested and valid." IAG says it has not worked with Magna Global.