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Monkeys and humans keep trying, even when we should give up

In a phenomenon known as the “sunk cost” effect, people follow through with things they have already invested in – even when those efforts are futile. Time invested in a relationship may cause us to stick with it longer than we should, while money dumped into a pointless project may encourage us to keep spending on it.

In a new study from Georgia State, experts have demonstrated that humans are not the only ones to engage in such potentially self-defeating behavior, and that monkeys also have a tendency to persist at tasks they have invested in.

The researchers have identified factors that could possibly play a role in the sunk costs effect. For example, humans and monkeys likely share an evolutionarily preserved mechanism that helps us balance the costs and benefits of our actions.

Both capuchin monkeys and rhesus macaques are housed at Georgia State’s Language Research Center. The monkeys participate in entirely voluntary and non-invasive cognitive and behavioral research, explained study co-author Professor Sarah F. Brosnan, who has worked with some of the monkeys for over 20 years. “They’re like my second set of kids.”

For the investigation, 26 capuchin monkeys and 7 rhesus macaques were trained to play a simple video game. Using a joystick, the monkeys attempted to move a cursor onto a moving target and hold it there as the target kept moving. 

If the monkeys were successful, they heard a victory sound and were given a treat. Those who were unsuccessful did not get a reward before moving on to a new round, which lasted either 1, 3, or 7 seconds. 

“Monkeys have really quick reaction times on these games, so one second to them is actually a long time,” explained Professor Brosnan.

Study lead author Julia Watzek noted that most of the rounds only lasted one second. “So if you didn’t get a reward after that, it was actually better to quit and start a new round. That would likely get you a treat sooner than if you had kept going.”

During the experiments, both species of monkeys showed sunk cost effects. “They persisted 5 to 7 times longer than was optimal, and the longer they had already tried, the more likely they were to complete the entire task,” said Professor Brosnan.

The researchers found that uncertainty had a big influence on persistence. When the monkeys got a signal that additional work was required, they were less susceptible to sunk cost behavior, but they still demonstrated it.

According to Watzek, studying this phenomenon in animals teaches us something about how their minds work, as well as our own. 

Professor Brosnan said the findings suggest that this behavior is likely driven by evolution and deeply embedded across species. “The epitome of the sunk cost is I’ve invested so much in this, I’m just going to keep going.” And this can really pay off when it comes to important tasks such as hunting prey, looking for a mate, or building a nest. “Sometimes, you just need to have patience.”

The research also indicates that human concerns – like not giving up on something we have publicly committed to – are probably not the main drivers of sunk cost behavior. The study is also a good reminder that there are times when you have good reason to give up.

“We’re predisposed to keep trying,” said Professor Brosnan. “And when we find ourselves sticking with things, we should also be a little reflective. Do I have a good reason to keep trying? Or should I leave with no reward, because it will save me more in the long run? That’s really hard to do. But hopefully we can use our cognitive abilities to help us overcome the emotional heartache of occasional sunk costs.”

The study is published in the journal Scientific Reports.

By Chrissy Sexton, Staff Writer

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