Jill Shelton, a postdoctoral psychology fellow at Washington University in St. Louis, went into classrooms at Louisiana State University posing as a student. Each time, her cell phone would ring, and she'd let it ring — in her handbag — for about 30 seconds. In some classes, she'd frantically search for the phone. Always to no avail.

You can imagine how annoying it must have been. What the other students didn't know was that they were part of a study. Later, they were tested on the content that was presented by the professor before the distraction and again during it.

Compared to a control group that was not interrupted, students who had endured the ring later scored about 25 percent worse.

In the situations where Shelton had also rummaged through her bag trying to silence the ring, the students tested even worse.

"Many of us consider a cell phone ringing in a public place to be an annoying disruption, but this study confirms that these nuisance noises also have real-life impacts," Shelton said. "These seemingly innocuous events are not only a distraction, but they have a real influence on learning."

In a separate test, students in a laboratory were tested on simple word-recognition tasks while exposed to a range of auditory distractions, including irrelevant tones, standard cell phone rings and parts of a song very familiar to most LSU students (an instrumental version of the LSU fight song).

"When we played the fight song as part of our lab experiments, the distraction factor lasted longer," Shelton said. "It slowed down their decision-making performance for a longer time than even a standard ring tone."

People who use popular songs as a personal ring tone may be increasing the odds their cell phone rings will be more distracting, Shelton figures.

"Depending on how familiar people are with these songs, it could lead to an even worse impairment in their cognitive performance," she said.

The effect dims with time, however.

Students in repeated trials of the experiment eventually were able to block the distracting effects of both standard and song-based cell phone rings, gradually reducing cognitive impairment caused by them.

"There's definitely some evidence to suggest that people can become habituated to a distracting noise," Shelton said. "If you're in an office where the phones are just ringing all the time everyday, it may initially be distracting to you, but you will probably get over it."

The results are detailed in the Journal of Environmental Psychology.