Why do they need a study at all? Multitasking makes you stupid. That's why everyone looks like a zombie on the way home from work on a weeknight.

Then, an hour or so after work ends, they're back to normal, except possibly very tired.

At the end they state

"Nass said that at the moment it is not clear if people with a predisposition to multitask are mentally disorganized, or if multitasking makes matters worse."

Which is a completely different conclusion to the one that this title would make you have :)

Send in the psychologist clowns to draw the wrong conclusions again.

This is not "multitasking". It's called being a distracted kid yammering away on social networking systems rather than doing real work. What do they really expect by concentrating on these "pre-med" (i.e. undecided), soon-to-drop-out, "fully-wired" college students, who probably never had concentration skills to begin with? Maybe this research would have some merit if they chose to widen the sample set to include people who normally aren't distracted and then put them into a distracting environment.

... sensory overload. Basically it's overloaded brain circuitry which diminishes the response of any given pathway.