For the first time, researchers have demonstrated the ill effects of mindless reading, a phenomenon in which people take in sentence after sentence without really paying attention.

Ever read the same paragraph three times? Or get to the end of a page and realize you don't know what you just read?

That's mindless reading. It is the literary equivalent of driving for miles without remembering how you got there, something so common many people don't even notice it.

In a new study of college students, researchers from the University of Pittsburgh and the University of British Columbia established a way to study mindless reading in a lab.

Their findings showed that daydreaming has its costs.

The readers who zoned out most tended to do the worst on tests of reading comprehension, a significant, if not surprising, result. The study also suggested that zoning out caused the poor test results, as opposed to other possible factors, such as the complexity of the text or the task.

The researchers hope their work inspires more research into why zoning out happens, and what can be done to stop it.

For now, they want the problem to be taken seriously.

"When you talk about this work at conferences, it does lend itself to a lot of jokes," acknowledges University of Pittsburgh professor Erik Reichle, co-leader of the study.

"It's so ubiquitous. Everybody does it," he said. "I think that's one of the main reasons it's been overlooked. And there's been a view that it is tough to study experimentally. Hopefully, now, there will be more interest in the topic."

The federal government is showing some.

Reichle and fellow psychology professor Jonathan Schooler did the study on a $691,000 grant from the Institute of Education Sciences, an arm of the Education Department. It is one of 178 federally backed projects aimed at giving schools a scientific basis for sound policies.

Over three experiments, students used computers to read the first five chapters of Leo Tolstoy's "War and Peace." (Reichle wanted some boring reading, better for zoning out.)

Reichle said the dry text itself did not skew the results toward mindless wandering. After all, the students were on alert, unlike the typical reader.

Participants were told to monitor and report instances of zoning out as they read text on a computer. Half of them got computer reminders, too: "Were you zoning out?"

Despite all that, many still reported zoning out at a regular pace.

"That's the amazing thing," Reichle said. "It shows how often this can happen even under conditions that are designed to keep it from happening."

The students said as their eyes scanned the words, their minds often were elsewhere.

They were hungry, or thirsty, or tired. They were thinking about plans, worries or memories. Some drifted into fantasies. Others stuck with the book, but their minds wandered into tangents about the plot.

Karen Wixson, a nationally recognized reading expert and professor of education at the University of Michigan, cautioned not to read too much into all this.

"This is a long ways away from having implications for reading instruction," Wixson said. "It could, eventually, down the line. But to draw inferences about this as a contributing factor toward reading comprehension would be a huge, huge leap."

To apply to younger kids, the target audience of reading classes, the findings would have to be replicated among school-age children, Wixson said.

She said participants may have zoned more often because they were reading off computer screens, and because they had no real incentive to pay attention, as they would in school.

But at the International Reading Association, Cathy Roller sees some direct payoff. She directs research and policy for the association, which represents literacy professionals.

By recognizing zoning out as problem, she said, teachers can do something.

Like asking students to put a checkmark next to paragraphs as they finish them and then summarize what they just read.

Or having students scan all the pictures and bold type before reading the text of a story, so that they have a general understanding of what's to come.

Zoning out may simply mean that the prose isn't interesting, Roller said. But it could also be a clear signal that students don't understand the work.

"You don't want to generalize narrow studies into large implications," Roller said. "But zoning out is probably not a whole lot different than not comprehending. And telling people to start using some good comprehension strategies is not likely to do any harm."

Roller knows. She had just been zoning out while reading a literature review.

By the way, last sentence here. If you missed anything, there's no shame in rereading.