Forget Ring Around the Collar. Forget those grinning cheerleaders of the Pepsi Generation hoisting cans of soda pop and smacking their lips. Forget the promises: jeans that fit better, cars that perform better, burgers that taste better.

The age of skepticism is nigh -- nowhere more obviously than among the nation's youth.

By high school graduation, the typical American has viewed an average of half a million television commercials. The result is the first saturated video generation: a group of restless, bored and sophisticated young consumers that has sent the $96 billion advertising industry scrambling for new strategies.

"They are pragmatists, as opposed to idealists," said Roger Enrico, president of Pepsi USA. "Maybe it's because they're the television generation, they're numb to marketing pitches. They don't believe everything they see. They can't be conned as easily."

"All the old gambits are off," said advertising executive Jerry Della Femina. "The new generation is very smart. They're not our victims. The strategy to reach them is not to try to snow them or manipulate them . . . . I can't sell Coppertone now by saying 'If you have a great tan, you'll meet the man of your dreams.' "

Using the developing science of "psychographics" -- categorizing people by life styles and values rather than by Census Bureau demographics of age, income and geography -- Madison Avenue researchers have found differences in the way 18- to 25-year-olds spend their money, in what grabs their attention and how they think.

This market of 32 million Americans -- a prized cohort because of its freewheeling consumerism -- is seen as an audience most responsive to a subtle sell, one for whom fast-moving images triumph over words, and music, sex and humor in advertisements are more effective than information.

Young people spend more money than ever before. More of BORN IN THE '60s Third of a Four-Day Series them work part time and full time; more of them do the family grocery shopping; more live at home, and those who marry have fewer children. Although their number dropped by 5 million in the last decade, teen-agers spent $49.8 billion in 1985 -- roughly the same amount, in constant dollars, as in 1975 but one-third more per capita.

With these high financial stakes, the science of marketing has become more sophisticated. "You don't sell a product by saying it gives you 23 percent fewer stomach aches," said Robert Pittman, president of MTV, cable television's music station. "You sell through emotional bonding, through images."

MTV has achieved its remarkable success (surveys show that half of all 12- to 34-year-olds watch it each week) by catering to a short attention span: It shows music videos -- two- to four-minute combinations of rock music and disjointed images -- 24 hours a day.

"Kids now watch television, listen to the radio and do their homework all at the same time." said Pittman, 32, the former disc jockey who built the network. "Their thinking is nonlinear. That's why MTV is nonnarrative. Images, sense, impressions are what count -- not words."

The trend is evident in political advertising. President Reagan's widely admired, image-laden ads in 1984 were created by a team that included Phil Dusenberry, who designed the Michael Jackson and Lionel Richie music video commercials that sent Pepsi-Cola sales skyrocketing last year.

Movies that appeal to the 18- to 25-year-old group, such as "Flashdance" and "Footloose," Pittman said, "sell mood and motion." Their favorite TV shows, such as "Miami Vice" and "Saturday Night Live," are fast-paced, "paying off" every two or three minutes with new action. A newspaper such as USA Today, heavy on graphics and short stories, is part of the trend.

If Reagan appeals to youthful voters, it is not because they share his social outlook, according to market researchers. "It's dead wrong to say this generation is more conservative," said Peter Kim, 27, a computer expert who taught sociology at New York University and now heads the research team at J. Walter Thompson, a major ad agency. "Every survey I've seen says their social values are as liberal as their counterparts in the 1960s and more liberal than older groups."

Young men say they expect their wives to work, and young women take career equality for granted, postponing marriage and children. Ads with housewives fussing over the dirt on their husbands' shirts are rarer. An American Express commercial shows a woman picking up the check after dinner with a man, a message in tune with the 35 percent of college students who use credit cards.

"They may not march for the ERA [Equal Rights Amendment], but 18-year-old women today want it all -- job, career and kids," Kim said.

"You can't compare the youth of the 1980s to the 1950s," said James Ogilvie, a researcher at SRI International, a firm that pioneered psychographic marketing. "What people do with their time, how they raise children is quite different. You have the decline of the nuclear family. Approval of premarital sex is way higher than in the 1950s. Attitudes towards war and peace and race relations are far different." A New Entrepreneurial Spirit

While surveys show that students are more preoccupied with making money, they also show the emergence of an entrepreneurial spirit, a willingness to take risks and a mistrust of institutions and corporations. A Pepsi commercial shows a youth setting up his own vending business on the beach. In a surrealistic Apple Computer ad, aimed at IBM and the corporate pack mentality, a long line of pin-striped business executives walk like lemmings to the edge of a misty cliff and topple off.

During the economically harder times of the '70s and early '80s, advertisers avoided comedy. But in the 1980s, particularly in commercials aimed at youth, humor has made a comeback. Godzilla, the campy Japanese film monster, is featured in at least four current campaigns, for Dr Pepper, Konica Film, Hallmark Greeting Cards and Scope mouthwash, for which he breathes steam onto burning buildings under the caption "Don't let your breath ruin a big night on the town."

Joseph T. Plummer, head of research for Young & Rubicam, sees in many of these ads -- humorous, sexually provocative, entrepreneurial, entertaining or emotionally grabbing -- one commercial and cultural manifestation of a "profound and enduring change in basic values." Young people look for "the unusual," he said. They are more "inner directed . . . . They value personal expression, creativity and strive for self-actualization."

Ogilvie echoes these observations, noting the growth of "the experience industry" -- travel, entertainment, cocaine and even evangelical religion, which he lumps together as evidence that young adults' consumerism is aimed less at buying material things that at trying to learn and experience new sensations. Ogilvie calls the new generation the "I-Am-Me's."

The J. Walter Thompson agency divides the younger market the "MTV Generation" (12 to 19), which is "living in a fast-paced world of sounds and images," and the "Baby Boomers" (aged 21 to 39). The agency's Peter Kim sees the 18- to 25-year-old group as far different from previous generations.

"They were too young for Woodstock and for the draft," he said. "Vietnam was a historical event. The social turmoil of the '60s that was pivotal for their older brothers and sisters is alien to them.

"What makes them unique is that they are children of the new technology -- the first to grow up with a whole new audio and visual environment, from cable to VCRs to computers. It is pivotal, because from an advertising perspective they are different in the way they process information. The strategies for reaching them have to be altered."

Twenty years ago, for example, New York City had four television stations, and viewers would accept passively 60-second commercials. Now the city has 37 channels and studies show that more than half the audience routinely deletes ads, switching channels or zapping them with VCR remote controls. The normal ad has shrunk from 60 seconds to 30 seconds, with 15-second spots becoming more common. A Restless Audience

"Young people are much more difficult to reach," Kim said. "The audience has grown more restless. Their attention span is shrinking -- it is hard for them to watch a two-hour feature film from start to finish. But their ability to grasp more bits of information at once has increased."

As a result, advertisements, movies and television shows aimed at a younger market have more "quick cuts," changes in scenery and camera position. Colors are brighter, the "visuals" more arresting. Commercials made by well-known movie directors with high-tech effects cost up to $1 million to produce.

"You have to give them 25 seconds of entertainment if you want them to listen to five seconds of advertising," said Della Femina.

Atlantic International, a Pennsylvania bank, hired the producer of "Miami Vice" to make a commercial showing a young couple zipping around a tropical landscape in a swank sports car. If "Hill Street Blues" with its realism and literate style reflects an earlier sensibility, "Miami Vice" embodies the changed values of youth in the '80s: The plot is incidental to the music and the images -- "a television more of sensation than of sense," as one critic put it.

In many ads aimed at young adults, the product is barely mentioned, or appears only briefly at the end of the ad. A recent campaign for Calvin Klein jeans showed models rambling on about their lives and self-doubts. The women said nothing about jeans, and the close-up shots barely showed that they were wearing jeans..

The sexual sell directed at the youth market is far more blatant. "Nothing comes between me and my Calvins," Brooke Shields' provocative message, sent teen-agers flocking to buy designer jeans.

Some ads have hardly any words at all. A recent Thunderbird commercial showed a series of lusciously photographed driving scenes, and only at the end does a voice come in to reveal the name of the car. The 18-minute movie Dusenberry produced on Reagan for the 1984 convention had no narrator.

At a recent news conference, Pepsi announced a new $50 million ad campaign with Michael Jackson. The reclusive star put in an appearance, but, in the spirit of subtle sell, the word "Pepsi" never passed his lips. Enrico said he wouldn't dream of asking Jackson -- who shuns beverages with caffeine -- to drink the stuff on camera.

"People would say 'Hey, give me a break,' " Enrico exlained. "Endorsements are old hat. We're trying to captivate people so they won't switch channels or zap the commercial. Our notion is entertainment . . . . It's not that Pepsi is Michael Jackson's favorite soft drink."

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