Maryanne Garry and Robert Michael of Victoria University of Wellington, New Zealand, and Irving Kirsch of Harvard Medical School in Boston said the powerful and persuasive effect that suggestion has relies on a person's "response expectancies," or the ways in which people anticipate responses in various situations.
These expectations set people up for automatic responses that actively influence how people get to the outcome expected, the researchers said.
"Once we anticipate a specific outcome will occur, our subsequent thoughts and behaviors will actually help to bring that outcome to fruition," the researchers said in the study. "If a normally shy person expects that a glass of wine or two will help him loosen up at a cocktail party, he will probably feel less inhibited, approach more people, and get involved in more conversations over the course of the party. Even though he may give credit to the wine, it is clear that his expectations of how the wine would make him feel played a major role."
The study authors pointed out "simply observing people or otherwise making them feel special can be suggestive," a phenomenon termed the Hawthorne effect. As a result, people might work harder, or stick to a task longer, the researchers said.
The findings were published in the journal Psychological Science.