Stanford researchers ran a series of experiments, hoping to find evidence that people who multitask have enhanced cognitive abilities that allow them to juggle multiple media effectively. Instead, they came away disappointed: The multitaskers were worse than a control group at everything they tested.

"We kept looking for what they're better at, and we didn't find it," said Ophir, the study's lead author and a researcher in Stanford's Communication Between Humans and Interactive Media Lab. …

"Th...