As headphones and earbuds become common in the workplace, sometimes even co-workers sitting next to each other are communicating online. iStockphoto.com hide caption

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Katherine Leon says she spends up to 12 hours a day online interacting with others who share her rare heart condition. Emily Bogle/NPR hide caption

itoggle caption Emily Bogle/NPR

This 2010 image, provided by IntelCenter, shows Humam Khalil Abu-Mulal al-Balawi in a posthumous video message posted on extremist websites. The al-Qaida double agent killed seven CIA operatives, a Jordanian spy and himself when he set off a bomb strapped to his body at a base in Afghanistan in December 2009. AP/IntelCenter hide caption

itoggle caption AP/IntelCenter

An image from a demo of the Stuck on Earth app, which Lauren Goode of All Things D calls "a photographer's dream." Stuck on Earth hide caption

itoggle caption Stuck on Earth

Couch-surfers pay for their lodgings with social interaction, not cash. studio tdes/Flickr hide caption

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