Researchers at Stanford University found that college students who made a habit of immersing themselves in various media at once were not very skilled at tests of memory, attention and, ironically, "task-switching."

In a nutshell, "they're terrible at multi-tasking," Dr. Clifford Nass, one of the researchers on the work, told Reuters Health in an interview.

The findings, published in the online edition of the Proceedings of the National Academy of Sciences, are surprising, the researchers admit.

The findings also suggest that today's array of devices that make multi-tasking possible, and supposedly easy, may not be a good thing.

Going into the study, Nass said, he and his colleagues assumed that "heavy multi-taskers" must have some innate ability that allowed them to handle several tasks at once.

Maybe they were good at filtering out irrelevant distractions from their environment, the researchers hypothesized.

But a simple cognitive test of such filtering - where test-takers were asked to focus on the characteristics of a group of red triangles while ignoring a few extraneous blue triangles - showed that multi- taskers performed more poorly than people who were not prone to media multi-tasking.

The same was true when study participants took a test that measures the brain's ability to organize and file away information, and when they took a test of task-switching. The multi-taskers were actually slower to shift their attention from one test task to another.

The study included 262 college undergraduates who filled out questionnaires on their media use - how often they went online, watched TV, read, listened to music, emailed and text-messaged, and how often they did a few of those things at once.

Students classified as either heavy or light media multi-taskers then took the series of cognitive tests.

While the results suggest that heavy multi-taskers are not actually good at what they do, the reasons for that are not clear, Nass said.

Overexposure to too many media distractions may be at fault - or it may be that people who are "born bad multi-taskers" are, ironically, more drawn to doing it.

It's possible, according to Nass and his colleagues, that heavy multi- taskers tend to have a generally "exploratory" orientation: they simply like to gather lots of information, even if that means sacrificing their performance on the task at hand.

But whether heavy media multi-tasking causes the differences seen in this study or not, Nass said, the implication would seem to be the same: "Heavy multi-taskers should stop doing it."

"Society is developing tools all the time to make multi-tasking easier," he said. "The question is whether that's a good thing."