An international team has found that monkeys trained to play computer games feel self-doubt and uncertainty and 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 suggests that our more primitive primate relatives are capable of such self- awareness, the `BBC` reported.
Prof John David Smith of State University of New York at Buffalo and Michael Beran of Georgia State University, trained the macaques to use a joystick-based computer game.
The animals were trained to judge the density of a pixel box that appeared at the top of the screen as either sparse or dense. To give their answer, the monkeys simply moved a cursor towards a letter S or a letter D.
When the animals chose the correct letter, they were rewarded with an edible treat. There was no punishment for choosing the wrong answer, but the game briefly paused, taking away -- for a few seconds -- the opportunity for the animals to win another treat.
But the monkeys had a third option -- choosing a question mark -- which skipped the trial and moved on to the next one. This meant no treat, but it also meant no pause in the game.
The scientists saw that the macaques used this option in exactly the same way as human participants who reported that they found a trial too tricky to answer; they chose to "pass" and move on.
Dr Smith presented footage of the animals playing the game at a session that was organised by the European Science Foundation.
"Monkeys apparently appreciate when they are likely to make an error. They seem to know when they don`t know," he was quoted as saying.
In the same trial, capuchins, which belong to group known as New World monkeys, failed to take this third option.
Dr Smith said: "There is a big theoretical question at stake here -- did (this type of cognition) develop only once in one line of the primates -- emerging only in the line of Old World primates leading to apes and humans?"
He said that the capacity think in this way was "one of the most important facets of humans` reflective mind, central to every aspect of our comprehension and learning".
"These results could help explain why self-awareness is such an important part of our cognitive makeup and from whence it came," he added.