Study suggests mice and rats, like humans, make poor choices based on 'sunk costs'

July 13, 2018 by Bob Yirka, Medical Xpress report

A team of researchers at the University of Minnesota has found that mice and rats, like humans, tend to make poor decisions based on "sunk costs." In their paper published in the journal Science, the group describes their study and what they found. Sarah Brosnan with Georgia State University offers a Perspective piece on the work done by the team in the same journal issue.

Most people are familiar with "sunk costs," and some of the behaviors associated with it. One example of a sunk cost is watching a movie to the end even when you're not enjoying it, simply because you have already invested so much time in it. Scientists study such behavior as a way of learning more about the and how it works. But, perhaps equally important, do other animals have similar traits? If so, that might indicate a for our behavior. In this new effort, the set up experiments to test whether mice and rats make poor choices just because they have invested time in them as well.

The experiments consisted of setting up a rodent food court with tasty pellet choices. A rat or mouse would then be introduced into the food court and observed to see how it responded. To add an element of sunk cost measurement, the researchers trained the rodents first to respond to different tones. One tone indicated how long they would have to wait for a given treat if they picked it. Another would serve as a countdown, letting them know how long they had to wait once they made a choice. The rodents were also given the option of abandoning a choice during their wait to go eat something else. The researchers found that both rats and mice would wait for a treat even if they knew a better one was available, regardless of how much waiting time lay ahead of them. They also found that the resolve of the rodents grew stronger the longer they waited. This, the researchers claim, shows that the rodents also made based on sunk costs.

Mice, rats and humans were trained to run equivalent foraging tasks. Left: a mouse foraging for food the Restaurant Row task. Right: a human foraging for videos on the WebSurf task. Credit: B.M. Sweis

The researchers also conducted an experiment in which they confronted humans with a choice of which videos to watch, and found that volunteers tended to remain resolute in waiting for a video to download once they had made the to view it—and became more resolved the longer they waited.

Explore further: All-they-can-eat diet for lab mice and rats may foster inaccurate test results

More information: B.M. Sweis el al., "Sensitivity to 'sunk costs' in mice, rats, and humans," Science (2018). … 1126/science.aar8644

Sunk costs are irrecoverable investments that should not influence decisions, because decisions should be made on the basis of expected future consequences. Both human and nonhuman animals can show sensitivity to sunk costs, but reports from across species are inconsistent. In a temporal context, a sensitivity to sunk costs arises when an individual resists ending an activity, even if it seems unproductive, because of the time already invested. In two parallel foraging tasks that we designed, we found that mice, rats, and humans show similar sensitivities to sunk costs in their decision-making. Unexpectedly, sensitivity to time invested accrued only after an initial decision had been made. These findings suggest that sensitivity to temporal sunk costs lies in a vulnerability distinct from deliberation processes and that this distinction is present across species.

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not rated yet Jul 13, 2018
"One example of a sunk cost is watching a movie to the end even when you're not enjoying it, simply because you have already invested so much time in it."

While this might work better explaining rat behavior, it isn't economically accurate. A better example of sunk costs would be watching the movie to the end because you paid to rent it. Once rented, the sunk rent cost remains constant whether you watch part, all or none of the movie. Watching an uninteresting movie because you have watched some portion - is more complicated and a poorer example in that it assumes time has a value that is related to the value of the rent.

Additionally, in humans there is a cultural component in some cultures ingrained to completing any task once started. The rat has no such cultural component.
not rated yet Jul 16, 2018
"While it may be a poor choice from the experimenters view. The animal is going to expend energy on a risky choice."

From the article: "The researchers found that both rats and mice would wait for a treat even if they knew a better one was available, ...". The other is known, so no risk.

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