Computers are extraordinary machines, able to perform feats of arithmetic that far exceed the capabilities of any human. They can store a huge quantity of data and recall it perfectly in the blink of an eye. They can even beat the chess world champion at his own game. So why do computers struggle to solve apparently simple tasks such as understanding speech, or translating text between languages? Why is a three-year-old child better at recognising everyday objects than the world’s most powerful supercomputer?