From mobile phones to instant messaging, Twitter to television and YouTube to Facebook, media multitasking has become a fact of modern life.

The increasing number of sources from which we get information at the same time, however, may be compromising our ability to focus on any of it and could actually be making it harder for us to multitask effectively.

With e-mails, phone calls, text messages and online social media all competing for our attention, often against a background of television, radio or music, our brains can reach information overload, research has suggested.

This appears to distract us from concentrating on particular activities, and also limits the ability to switch from one job to another — a key element of the multitasking that media omnivores often claim as their great strength.

The study, led by Clifford Nass, of Stanford University in California, is among the first to investigate whether cognitive abilities might be affected by the range of media that people regularly use. The results are published in the journal Proceedings of the National Academy of Sciences.

“With the diffusion of larger computing screens supporting multiple windows and browsers, chat and SMS, and portable media coupled with social and work expectations of immediate responsiveness, media multi-tasking is quickly becoming ubiquitous,” the scientists wrote. “These changes are placing new demands on cognitive processing, and especially on attention allocation.”

The scientists first used a questionnaire to assess how often people used 12 different information sources: print media, television, computer-based video such as YouTube and iPlayer, music, non-music audio, video games, phone calls, instant messaging, text messaging, e-mail, web surfing and computer-based applications such as word processing.

The results were used to identify heavy and light “media multi-taskers”, depending on the frequency with which they used these tools concurrently. People from each group were then given a range of cognitive tests.

In the tests, subjects had to concentrate on a core task, such as determining whether red rectangles on a computer screen had changed in orientation. For some exercises they were also shown distracting information, such as blue rectangles among the red ones, which they were supposed to ignore.

There were few differences between heavy and light media multitaskers on the basic tests, but when distractions were involved the heavy media multitaskers took significantly longer to respond correctly.

A second set of tests then assessed the subjects’ ability to switch from task to task — in this case, between a letter-based exercise and a number-based one. The heavy media multitaskers again took significantly longer to make this switch successfully.

In each case, the heavy media multitaskers had more trouble filtering out irrelevant information, whether it was the distracting stimuli or the second task that was not being prioritised.

This might reflect the way that their brains have become primed to concentrate simultaneously on information from a wide variety of sources, which makes it harder for them to focus on a single important job or to switch effortlessly from one task to the next.

Heavy media multitaskers “may be sacrificing performance on the primary task to let in other sources of information”. Light media multitaskers, by contrast, “may find it easier to attentionally focus on a single task in the face of distractions.”

Further research in this field was essential, the researchers added, given the increasing proliferation of media sources that were commonly used at once.

“In an ever-more saturated media environment, media multi-tasking ... is becoming an increasingly prevalent phenomenon, especially among the young . . .

“This issue seems especially pertinent in light of evidence that human cognition is ill-suited both for attending to multiple input streams and for simultaneously performing multiple tasks.”

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