The 14-year-old has a very simple decision to make. When he sees a light out of the corner of his eye he is supposed to ignore it and keep looking straight ahead. It seems extraordinarily easy — even eight-year-olds can do it correctly half of the time — but it requires reigning in a natural impulse to look. And every parent of a teenager knows that reigning in impulses is not their strong suit. In this simple test, the teenager performs as well as adults do. But a peek inside his head reveals that he puts a lot more work into it. His brain uses a whole host of frontal regions — those involved in planning and executing actions — that adults ignoring something in their peripheral vision just don't need.
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