Photo

If you have just read the same paragraph 12 times because the person sitting next to you on the bus is chatting on her cellphone, feel free to show her this: scientists have found another piece of evidence that overheard cellphone conversations are far more distracting and annoying than a dialogue between two people nearby.

In a study published Wednesday in the journal PLoS One, college students who were asked to complete anagrams while a nearby researcher talked on her cellphone were more irritated and distracted — and far more likely to remember the contents of the conversation — than students who worked on the same puzzles while the same conversation was conducted by two people in the room.

The study is the latest in a growing body of research on why cellphones rank so high on the list of modern irritants. Mounting evidence suggests that the habits encouraged by mobile technology — namely, talking in public to someone who is not there — are tailor made for hijacking the cognitive functions of bystanders.

One reason, said Veronica V. Galván, an assistant professor of psychology at the University of San Diego and the lead author of the study, is the brain’s desire to fill in the blanks.

“If you only hear one person speaking, you’re constantly trying to place that part of the conversation in context,” Dr. Galván said. “That’s naturally going to draw your attention away from whatever else you’re trying to do.”

It is also a control thing, Dr. Galván and her colleagues said. When people are trapped next to a one-sided conversation — known nowadays as a “halfalogue” — their anger rises in the same way it does in other situations where they are not free to leave, like waiting for a train.

“If you’re waiting in line and someone behind you is talking on a cellphone, you’re kind of stuck there,” she said, “and you can have a psychological stress response.”

Not that you have to feel stressed to find cellphones disruptive. Students in a 2010 Cornell study had trouble completing modest tasks, like tracking a dot on a screen with a cursor, while listening to a tape of a one-sided conversation, even though they knew the conversation was the focus of the study.

The 149 students in Dr. Galván’s study did not know the side conversations were part of the research; 15 students who did figure it out were not counted in the results. And while their ability to solve the anagrams was not noticeably impeded, the students listening to the halfalogues scored higher when rating themselves on a “distractibility scale.” They also said that they remembered more specifics from the conversation, which was the same script in both cases (a theater professor was enlisted to facilitate the deception).

The brain simply can’t ignore a stream of desultory new information, said Lauren Emberson, the postdoctoral associate at the University of Rochester, New York, who led the Cornell study when she was working there.

“Our brains are set up to focus on things that are novel or unexpected,” Ms. Emberson said. “When you’re listening to one half of a conversation, every new utterance is a surprise, so you’re forced to constantly predict what’s going to happen next.”

Because it is next to impossible to tune out a nearby cellphone conversation, people subjected to them often believe — incorrectly — that the talker is being abnormally loud, according to findings from a 2004 study from the University of York, England. Sixty-four commuters were exposed to the same conversation at different volume levels, half as a cellphone call and half as a face-to-face talk. On average, the commuters thought the mobile phone talkers were louder, even when they were not.

“When you stare at a light, it seems brighter,” said Dr. Emberson. “And when you can’t not pay attention to a noise, it seems louder.”

That sense of being subjected to something unavoidable and unpleasant has turned public cellphone conversations into a flash point.

“When you are overhearing some stranger’s inane cellphone conversation, your brain has to work a lot harder at what you’re doing, and it interferes with your ability to focus on other things,” said Amy Alkon, a syndicated columnist who wrote a book about manners called “I See Rude People.” “It gives you what I call a ‘neural itching.’ ”

Though surveys have repeatedly placed public cellphone conversations at the top of Americans’ pet peeves, there are indications that the problem is easing — or, perhaps, that people are starting to accept that all this yakking is the new reality. In 2006, 82 percent of Americans said they were at least occasionally annoyed by cellphone conversations in public. In 2012, that number dropped to 74 percent.

Ms. Alkon attributes the drop to a rising rejection of the behavior. “People are starting to recognize that it’s really rude to force other people to listen to your conversation,” she said, “especially in places where you’re trapped, like a train or a doctor’s office.”

It is a feeling familiar to anyone who has tried to read, work or even just relax on public transportation. Geoff Huntting, a marketing executive from New Canaan, Conn., says his hour-plus commute to Manhattan is often tarnished by a cellphone talker.

Like the students in Dr. Galván’s study, he said he could still remember the details of an annoying halfalogue he overheard more than a month ago. “This girl in her late 20s was complaining to her boyfriend or significant other — at full volume for the entire ride — about this other girl at work who was trying to score points with the boss or something,” said Mr. Huntting, 38

To be fair, he said, the train is also frequently filled with loud, intoxicated Yankee fans heading home after a game. But he somehow finds it easier to tune out those conversations.

“It’s loud, but it’s less annoying than hearing this on-and-off complaining about something you can’t put into context,” he said. “It’s not even a conversation — it’s prattle, it’s just noise.”