When Clifford Nass moved to a Stanford University freshman residence hall as a "dorm dad" in 2007, he wasn't quite prepared for college life in the 21st century. Even as a professor who for decades had studied the interaction of humans and computers, he was caught off-guard when one of his students explained why she was texting her boyfriend just down the hall.

"It's more efficient," she said.

Then there was a familiar sight Nass continued to find astonishing. In lounges, in libraries, just about everywhere, he gazed at a legion of the perennially plugged-in: They chatted on cellphones, scanned Facebook, watched videos, blasted out tweets, and maybe even thumbed through a calculus text or a history of the modern world, all at once.

"I thought: Wow, that's pretty awesome," he told The Boston Globe in 2011. "What do they know that I don't know, and how can I be like that?" The answers surprised him.

Nass, a sociologist who was among the first academics to sound alarms about the dangers of chronic multitasking and the decline in the kind of face-to-face interactions that he so unabashedly enjoyed with students and colleagues, died Saturday at Stanford Sierra Camp near South Lake Tahoe, Calif. He was 55.

Nass collapsed after a hike, the university said.

After several years of studies, Nass and other Stanford researchers came to some disturbing conclusions. They found that the heaviest multitaskers -- those who invariably said they could focus like laser beams whenever they wanted -- were terrible at various cognitive chores like organizing information, switching between tasks and discerning significance.

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"They're suckers for irrelevancy," he said. "Everything distracts them."

More worrisome to Nass was his finding that people who regularly jumped into four or more information streams had a tougher time concentrating on just one thing even when they weren't multitasking. By his estimate, "the top 25 percent" of Stanford's students were in that category.