"What I'm saying is that culturally we need a much better balance. We need more of a yin and yang between [introverts and extroverts]." - Susan Cain James Duncan Davidson/TED hide caption

itoggle caption James Duncan Davidson/TED

Environmentalist John Francis speaks about the 17 years of his life during which he never spoke a word. Andrew Heavens/Courtesy of TED hide caption

itoggle caption Andrew Heavens/Courtesy of TED

"I began to learn at least what other people felt and what they wanted to say before cutting them off with my own diatribe. I used to do that." - John Francis Andrew Heavens/TED hide caption

itoggle caption Andrew Heavens/TED

In sighted people, the part of the brain that recognizes faces is linked to the brain's visual system. But in blind people it seems wired to circuits that process sound. Tina Zellmer/Ikon Images/Corbis hide caption

itoggle caption Tina Zellmer/Ikon Images/Corbis

A tangle of protein (green) in this scanning electron micrograph of a brain cell of an Alzheimer's patient lies within the cytoplasm (blue) of the cell. The tangle consists of clumps of a toxic form of tau. Thomas J. Deerinck/Corbis hide caption

itoggle caption Thomas J. Deerinck/Corbis

The Rosetta spacecraft, which orbits the comet, captured this series of images of the Philae lander bounding off the surface. The precise spot the lander came to a stop remains unknown. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA hide caption

itoggle caption Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

Sherri Erkel and her daughter, Asa, cook dinner in their kitchen in Iowa City, Iowa. The Erkel family is part of an EPA study measuring the amount of food wasted in U.S. homes. Pat Aylward/NET News hide caption

itoggle caption Pat Aylward/NET News

A global positioning receiver on the top of a combine harvester at a farm in Warwick, Md., in June. The equipment uses sensors and computers to help drive the combine along the route where the crops were planted, judge the composition of a crop and generate crop yield reports. Brendan Smialowski/AFP/Getty Images hide caption

itoggle caption Brendan Smialowski/AFP/Getty Images