Can you think of 100 different uses for a sock? How would you cope with glasses that turn everything upside down? What's your emotional intelligence? Can you create a work of art in ten minutes?

Horizon takes seven people who are some of the highest flyers in their field - a musical prodigy, a quantum physicist, an artist, a dramatist, an RAF fighter pilot, a chess grandmaster and a Wall Street trader. Each is put through a series of tests to discover who is the most intelligent?

The principle way that we measure intelligence, the IQ test, remains popular and convenient. Yet most psychologists agree that it only tells half the story... at most. Where they disagree is how to measure intelligence, for the simple reason that the experts still don't know exactly what it is.