Some even started giving themselves electric shocks as the minutes ticked by.
"I think many of them were trying to shock themselves out of boredom," said psychologist Timothy Wilson of the University of Virginia. "It's just a sign of how difficult (being alone with one's thoughts) can be for people.... This isn't something that most people find really enjoyable."
At least, that's the case for people not trained in techniques like meditation, Wilson and co-authors say in a paper released Thursday by the journal Science.
In a series of experiments, college students left their cellphones and other distractions behind and spent six to 15 minutes alone in a sparsely furnished room on campus. They were told to entertain themselves just with their thoughts, or imagine doing one of three pleasant activities like hiking.
The experience was not exactly heaven. On a 9-point scale of enjoyment, their average rating was about in the middle. And about half the participants gave it a rating at the half-way mark or below.
In nonscientific terms, the overall verdict was: Eh.
Doing it at home proved no more enjoyable. When the researchers had 61 people from the community try it at home, about half admitted to cheating by doing things like checking their cell phones, writing or doodling. Their overall results were about the same as with the students.
The most startling experiment involved the electric shock. Students first shocked themselves in the ankle and rated how unpleasant that was. They were asked to imagine being given $5 and to specify how much they would pay to avoid another shock, or to receive one. Then they were told that if they wanted to, they could shock themselves again during their time alone, which ran 15 minutes.
Of the 55 participants, 42 said they would pay to avoid feeling the shock again. But once they were left alone, even some of these volunteers chose to shock themselves anyway; 12 of 18 men and six of 24 women.
Wilson was surprised by the overall results. When the experimenters began the study, "it seemed that it shouldn't be that hard for people to use (their brains) to entertain themselves," he said. "All of us have pleasant memories we can call upon, we can construct stories and fantasies."
Maybe the problem is that while pleasant thoughts pop up naturally while we're doing something like driving or exercising, it's hard to activate them on demand, he said.
"I think it's an issue of mental control. The mind is built to engage in the world and when you give it nothing to engage it, it's hard to keep one train of thought going for very long."
In any case, the result is probably not a consequence of modern-day life, Wilson said, because even in medieval and ancient Roman times, there were complaints that people don't take enough time to contemplate.
Jonathan Schooler, a psychologist at of the University of California, Santa Barbara, who didn't participate in the work, said he found the results "surprising and in some ways a disappointing statement about human nature."
Most people have interesting things to think about "so I don't understand why they find themselves such bad company," Schooler said.
"This is innovative new research, which means it's the beginning of our understanding of this phenomenon, and not the end," Schooler said.