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I'm convinced there's a cliche to describe every academic speciality. People meet an English professor and they say, "Gee, I'd better watch my grammar." If you introduce yourself as a mathematician, someone will comment, "I can't even balance my checkbook."

For folklorists, a typical reaction is, "It must be great to make a living collecting jokes."Grammar patrol, computational whiz and joke collector sum up what many assume these jobs are all about.

For psychologists, the line might be, "You must be an expert in subliminal persuasion."

Lots of people "know" that psychologists have developed brainwashing techniques that advertisers misuse, and the best-known example is "The Popcorn Experiment."

Psychology professor Anthony R. Pratkanis of the University of California, Santa Cruz, recently asked a manufacturer of subliminal self-help audio tapes for evidence that they work, and the man replied, "Don't you know about the study they did where they flashed `Eat Popcorn and Drink Coke' on the movie screen?"

The version I heard years ago was that images of hot, buttered popcorn were flashed quickly on the screen during feature movies, leading to a boom in sales from receptive viewers. My understanding was that the original experiment with subliminal selling occurred in the 1930s.

Later I learned that the "popcorn" report actually came from businessman James Vicary, who said he tested the technique during screenings of the film "Picnic" for six weeks in 1956 at a theater in Fort Lee, N.J. The messages were "Eat Popcorn" and "Drink Coke," and the claimed increase in sales was about 18 percent for Coke and 58 percent for popcorn.

Pratkanis analyzes the Vicary case and similar claims in his article in the spring 1992 issue of Skeptical Inquirer magazine devoted to myths of subliminal persuasion.

In a nutshell, Pratkanis reports, psychologists have found no evidence that subliminal messages will alter behavior. The Vicary study, announced in a press conference in September 1957, was never described in professional literature and has not been successfully replicated.

The best published account of "The Popcorn Experiment," writes Pratkanis, appeared in Senior Scholastic magazine, a periodical written for junior high school students.

Vicary's claims set off a storm of protests and led to government prohibition of subliminal advertising. In 1962, Vicary admitted that he had actually done little research and that his database was "too small to be meaningful."

Although "The Popcorn Experiment" was debunked by the profession and discredited by its instigator, it is a story with a life of its own. Many still hear of it in high-school or college classes or read about it in textbooks or articles.

Pratkanis calls it "faulty faith" that people will accept such claims as being the results of a careful application of the scientific method. There's also an element of urban legend tradition involved, since the story changes each time it's told.

For example, not only do the dates and methodologies for the experiment vary, but some people say popcorn sales hit "an all-time record," or that sales of Pepsi or another soft drink died in the theaters involved.

Some people add the questions "Hungry?" and "Thirsty?" to their description of the experiment, while others say that both an image of the products and the words of a sales message were flashed on the screen. I've also heard that the experiment took place in a drive-in theater where car doors began slamming as patrons headed for the refreshment stand.

I've read of two updates on subliminal persuasion that sound suspiciously like legendary exaggeration. A 1979 article in Time magazine said anti-shoplifting messages just below the threshold of hearing in the music played in department stores had cut theft losses.

Another claim, made in a 1987 article in the Los Angeles Times, was that workers were exposed to subliminal messages like "Work faster" flashed on their computer screens.

The psychologist's response to such claims is that subliminal perception can be proven, but subliminal persuasion is a myth. The folklorist adds that scientific ignorance, whatever its source, often leads to some creative stories."Curses! Broiled Again," Jan Harold Brunvand's fourth collection of urban legends, is now available in paperback from Norton. Send your questions and urban legends to him in care of the Deseret News.

1992 United Feature Syndicate Inc.