Turns out humans aren't the only ones that can't let it go

Everyone has faced the dilemma of the grocery line — scanning multiple checkout aisles before wheeling a cart into one, then staying grumpily in place even when a shorter line opens up.

Turns out, these aren't just quirks of Scandinavian stubbornness.

A new study by researchers at the University of Minnesota has found that people and animals alike are hard-wired to make choices this way. Published in the prestigious Science journal, the study showed that humans and mice are prone to "precommitment" decisionmaking, or delaying initial choices, perhaps for fear of regret. Then they experience the "sunk cost" effect, by which they stick with decisions even when better options come along.

Understanding these ingrained behaviors could affect everything from stock investing to medical treatments — maybe even grocery shopping.

"The right thing to do is get in line and then see if another line is moving faster" and switch, said David Redish, a U neuroscience professor who co-authored the study. "Nobody does that."

The researchers also found no relationship between the two decision stages — the length of precommitment deliberations did not affect whether people stuck with their decisions. People might take seconds or minutes deciding which restaurant to try in a food court. But once they choose, they won't switch even if someone walks by with a favorite food they want more.

In businesses, people who have invested millions in a project are likely to stick with it even when new opportunities appear to have a better payoff.

The sunk cost effect has been proven in research for decades, but was thought to exist only in humans — and then only in adults. It basically proves that people confer a value on past investments — such as time spent in line — even when they have no actual value for future decisions.

The U's researchers created a model to test whether mice and rats also exhibit this behavior. They created a maze with several stops where mice could learn how long they would need to wait for food, based on changing beep tones, and what types of food were available, based on wall patterns. But to get food, they had to take the extra step of entering a waiting area. Time in the maze was limited, creating economic pressure to make quick value decisions.

Finding a comparable human experiment was tougher. Mice forage for food, the researchers reasoned, but what did humans search for each day?

"Kitten videos," one researcher blurted out at a meeting.

An idea was born. Researchers had study participants choose certain types of video clips, such as panoramic scenes or animal videos, and then decide whether to wait for them based on varying download times. The participants ranked the videos, so researchers could study how preferences affected their decisions as well.

Proving that this effect was common to animals and humans was important, the researchers said, because it suggests it's a common, biological response more than a product of human experience.

Some believe that adults stick with their decisions to avoid embarrassment in front of friends or other people, but that doesn't apply if mice are doing the same thing, Redish said.

"I'm pretty sure the rats and mice are not sitting there not wanting to look stupid in front of their friends," he said.

Animals and humans share the feeling of regret, and Redish theorized that they pause initially because they don't want to regret decisions later, and because they know they are unlikely to back out of the decisions they make.

Researchers have been studying the underpinnings of human decisionmaking for centuries, but from limited views. Economists have studied how emotion affects stock market picks, but "they don't necessarily know how the brain processes that information," Sweis said.

The findings could have a broad impact on important human decisions. The sunk cost effect could, for example, prevent people with addictions from reversing their destructive choices. But some studies have shown that a different part of the brain can be taught through exercises to intervene and overcome decisions that appear irreversible.

"Decisions depend on neural circuits, which means that manipulating those circuits changes the decision process," said Mark Thomas, a neuroscience and addiction researcher who was part of the study.

The study had limitations, including that it compared an essential task such as eating in mice with a recreational task such as watching videos in people. It also studied decisions only in ideal conditions, which could change if animals or people experienced health problems or stress.

In a review accompanying the Science article, Georgia State University neuroscientist Sarah Brosnan said the research made important advances in studying the trade-off between making a choice and risking an error.

"Understanding this evolutionary trade-off," she wrote, "can help us to better understand why humans make the decisions that we do and, ultimately, suggest ways of improving human decisionmaking."