Monkeys Believe in Winning Streaks Like Us

1367 Monkeys Believe in Winning Streaks Like Us
Sarah Heilbronner via Rochester

Sometimes you feel like you’re on a roll, while other times you’re down in a slump. Even in random situations, humans tend to see winning and losing streaks. Scientists disagree about whether this behavior -- called “hot-hand bias” -- is an artifact of our culture or if it’s deeply ingrained. According to a new study, monkeys share our unfounded belief in a good run of luck -- and food may be to blame.

“If a belief in winning streaks is hardwired, then we may want to look for more rigorous retaining for individuals who cannot control their gambling,” Benjamin Hayden from the University of Rochester says. “And investors should keep in mind that humans have an inherited bias to believe that if a stock goes up one day, it will continue to go up.”


To study systematic error in decision making in primates, Hayden and colleagues created a computer game that entertained monkeys for hours on end. “Luckily, monkeys love to gamble,” says Tommy Blanchard also of Rochester

Three rhesus monkeys had to choose right or left, and when they guessed correctly, they were rewarded. There were three types of play. Two had clear patterns, where the correct answer would repeat on one side or alternate side to side; in the third play, the lucky pick was totally random. In scenarios where a clear pattern exists, the monkeys quickly guessed the correct sequence. But in the random case, they continued to make choices as if they expected a streak: Even when rewards were random, the monkeys still favored one side. (Luck be a monkey?)

After an average 1,244 trials for each play, the monkeys showed the hot-hand bias consistently over weeks of play. “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,” Blanchard explains in a news release. Their results suggest that the penchant to see patterns that don’t exist may be inherited. 

The researchers speculate that it’s an evolutionary adaptation that offered some advantage to our ancestors when they were out foraging for food -- since the distribution of resources in the wild isn’t random. “If you find a nice juicy beetle on the underside of a log, this is pretty good evidence that there might be a beetle in a similar location nearby, because beetles, like most food sources, tend to live near each other,” Hayden explains.


Evolution, it seems, has primed our brains to look for patterns. “We have this incredible drive to see patterns in the world, and we also have this incredible drive to learn,” he adds. “If there’s a pattern there, we’re on top of it. And if there may or may not be a pattern there, that’s even more interesting.” 

The work was published in Journal of Experimental Psychology: Animal Learning and Cognition


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