What did market researcher james vicary do in 1957 that made people concerned about subliminal manipulation?

In 1957, James Vicary falsely claimed that he conducted an experiment on 45,669 individuals who are moviegoers at New Jersey theater. He reported that it exposed the individuals to a split second advertising of pop corn and coca cola and that this dramatically increased the amount of pop corn and coca cola that was sold. This type of advertising is called subliminal manipulation. It was later discovered that James was lying.

James Vicary claimed in 1957 that he exposed a movie theater audience to very fast, flashing images displaying popcorn and Coca Cola, and similar messages telling them to buy these items. He claimed that these subliminal messages, messages communicated subtly without the recipient even being fully conscious of them, boosted popcorn and Coke sales. 

While this had a large impact on people's knowledge and perception of the topic, it later turned out that James Vicary likely made the whole experiment up.