Monkeys trained to play computer games have helped to show that it is not just humans that feel self-doubt and uncertainty, a study says.

US-based scientists found that macaques will "pass" rather than risk choosing the wrong answer in a brainteaser task.

Awareness of our own thinking was believed to be a uniquely human trait.

But the study, presented at the AAAS meeting in Washington DC, suggests that our more primitive primate relatives are capable of such self-awareness.