In a nutshell: These researchers have found a way to quantify confidence.

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The big picture:

Survival, for most animals, hinges on making good decisions on the fly in changing, uncertain surroundings.

In this study, the researchers were able to get a handle on the confidence rats had in those decisions.

“Mostly choice itself has been studied. But we were interested in what happens before a choice and after,” says CIBF chief investigator Ehsan Arabzadeh of the Australian National University, who led the team.

In sessions of about 25 minutes, the rats were allowed to drink from either of two spouts that delivered a set amount of sugary water with different probabilities — 80 percent of the time versus 20 percent of the time. Within a couple of sessions, the rats had learned to rush to the spout that was most likely to work.

Next, an element of uncertainty was introduced that more closely mimicked real life: the sugary water was delivered with the same probabilities but after unpredictable amounts of time. In the face of that uncertainty, the rats had to decide whether to persist with their choice or to abandon it. The higher the likelihood of reward, the more they persisted, pursuing the more profitable choice for between 50 and 300 extra milliseconds.

“Confidence is introspective, so it’s hard to rate even in humans,” says Arabzadeh.

“But we found confidence can be quantitatively measured in rats by the time spent pursuing a particular choice.”

In a second set of trials, two spouts provided sugary water, again with different probabilities, but this time the sugary water would stay in a spout until the rat drank it.

Once again, when the element of uncertainty was introduced by changing delivery times, the rats were more confident about choosing the spout that offered the most sugary water. At the same time, they were able to keep a running tally, feeding repeatedly from the high-likelihood spout, and then periodically going to the low-likelihood one — which with time became increasingly likely to contain sugary water — for a bonus.

“It’s striking. Even with such a complicated task, they choose the optimal strategy,” says lead author Justine Fam of the University of New South Wales. “One explanation is that the rats are able to keep the information in their working memory to act on later.”

Next steps:
The team is now exploring similarities and difference in confidence in decision-making between species, including humans

Fam, J., Westbrook, F., & Arabzadeh, E. (2015). Dynamics of pre-and post-choice behaviour: rats approximate optimal strategy in a discrete-trial decision task. Proceedings of the Royal Society of London B: Biological Sciences, 282(1803), 20142963.

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