Editor’s Note: We dug into why government, think tanks, and media coverage may focus more on right-wing extremists than left-wing groups, in part because of reader queries. This is part of our ongoing ...

Here is one version of the left-right spectrum, as described in 1975 by a former Barry Goldwater speechwriter who had left the conservative movement to break bread with Black Panthers and Wobblies.

Some of the most complex cognitive functions are possible because different sides of your brain control them. Chief among them is speech perception, the ability to interpret language. In people, the ...