Monkeys are keen gamblers who share our unfounded belief in winning and losing streaks, a new study has found.
Humans have a well-documented tendency to see winning and losing streaks in situations that, in fact, are random.
But scientists disagree about whether the "hot-hand bias" is a cultural artifact picked up in childhood or a predisposition deeply ingrained in the structure of our cognitive architecture.
In the first study in non-human primates of this systematic error in decision making, researchers found that monkeys also share our unfounded belief in winning and losing streaks.
The results suggests that the penchant to see patterns that actually don't exist may be inherited - an evolutionary adaptation that may have provided our ancestors a selective advantage when foraging for food in the wild, according to lead author Tommy Blanchard, a doctoral candidate in brain and cognitive sciences at the University of Rochester.
The cognitive bias may be difficult to override even in situations that are truly random, said coauthor Benjamin Hayden, also from Rochester.
To measure whether monkeys actually believe in winning streaks, the researchers created a computerised game that was so captivating monkeys would want to play for hours.
"Luckily, monkeys love to gamble," said Blanchard.
The team devised a fast-paced task in which each monkey could choose right or left and receive a reward when they guessed correctly.
The researchers created three types of play, two with clear patterns (the correct answer tended to repeat on one side or to alternate from side to side) and a third in which the lucky pick was completely random.
Where clear patterns existed, the three rhesus monkeys in the study quickly guessed the correct sequence.
But in the random scenarios, the monkeys continued to make choices as if they expected a "streak." In other words, even when rewards were random, the monkeys favoured one side.
The monkeys showed the hot-hand bias consistently over weeks of play and an average of 1,244 trials per condition.
"They had lots and lots of opportunities to get over this bias, to learn and change, and yet they continued to show the same tendency," said Blanchard.
The finding was published in the Journal of Experimental Psychology: Animal Learning and Cognition.
