FRIDAY, May 21, 2010 (HealthDay News) -- If you've ever wanted to shout "shut up!" while listening to someone else's cell phone conversation in an elevator, train or restaurant, new research reveals why.
Overhearing one-sided conversations really is more annoying because the brain finds it more taxing, and therefore more distracting, to listen to only half of a conversation versus the whole thing.
"It's unbelievably irritating to overhear someone on a cell phone," said lead study author Lauren Emberson, a doctoral candidate in psychology at Cornell University in Ithaca, N.Y. "It's harder to tune out, you can't pull your attention away from it and you're more distracted by it.
Emberson and her colleagues did a series of experiments in which college students were asked to do certain tasks that required their full attention while listening to recordings of female college students having a conversation about a current event or other topic. The students were told to ignore the recording as best they could.
In one task, students had to follow a moving dot on a computer screen with a mouse. In another task, they had to remember a series of four letters and were told to press a button each time one flashed on a screen and not to press the button when other letters flashed.
Students first did the tasks in a silent room to determine their baseline proficiency.
When researchers had them do the same tasks while listening to a dialogue, they did just as well as they did in the silent room. They also did well when listening to a monologue, or one person recounting an earlier conversation.
But when researchers played only one side of the dialogue -- similar to overheard cell phone chatter -- the number of errors students made on the attention tasks spiked.
The research will appear in a upcoming issue of the journal Psychological Science.
In some respects, the findings are curious, Emberson said, because when overhearing half a conversation you're actually hearing less sound than you'd hear while listening to a full conversation.
But much of how humans process language is based on the brain's ability to predict, or anticipate, what comes next in a sentence, Emberson said. The brain is attuned to patterns of speech, acoustics and grammar, so when someone says, "I like to eat", the brain is already figuring out that what comes next is probably going to be some type of food.
One-sided conversations make it more difficult for the brain to make these predictions, so listening is more distracting, she said.
"With half a conversation we get less information, so we have to listen more," Emberson said.
It's not just in speech that humans count on being able to predict what's going to happen next, said Gerry Altmann, a professor of psychology at the University of York in England.
"There is increasing research in a whole range of areas to do with human behavior that shows our ability to predict what's going to come next is fundamental to both our mental and physical functioning," Altmann said. "Much of the behavior we engage in is, in fact, very predictable."
Altman likened hearing half a phone conversation to the difference between walking on a smooth sidewalk to an uneven, rock-strewn path. One doesn't require much attention. The other, which is unpredictable, requires more attention. An overheard cell phone conversation is different in that much of the process is subconscious, he added.
"With half a phone conversation, you're only getting a snapshot, so you can't predict the future, which is what the brain has evolved to do," Altmann said.
And with some 285 million cell phone subscribers in the United States, it's an irritation that isn't likely to go away.
The National Science Foundation has more on how the brain processes language.