How to optimize decision-making?

UNIGE researchers show that our brains do not make decisions based on their intrinsic value, but for what they offer far beyond the other possible propositions.

Our brains are constantly confronted with different choices: should I have a chocolate flash or a macaroon? Do I have to take the bus or go by car? What should I wear: a wool or cashmere sweater? When the difference in quality between two choices is large, the choice is made very quickly. But when this difference is negligible, we can be stuck for a few minutes at a time, or even longer, before we can make a decision. Why is it so difficult to make a decision about two or more choices? Is it because our brains are not optimized for making decisions? In an attempt to answer these questions, neuroscientists at the University of Geneva (UNIGE) in Switzerland – in partnership with Harvard Medical School – have developed a mathematical model of the optimal choice strategy. They have shown that optimal decisions should not be based on the real value of the choices but on the difference in value between them. The results, which you can read in the newspaper Nature Neuroscience, show that this decision-making strategy maximizes the amount of reward received.

There are two types of decision-making: first, there is perceptual decision-making, which is based on sensory information: do I have time to cross the road before the car approaches? Then there is a decision-making based on values, when there is no good or bad decision as such but it is necessary to choose between several proposals: I want to eat apples or apricots? When making value-based decisions, choices are made very quickly if there is a big difference in value between different proposals. But when the proposals are similar, decision-making becomes very complex even if, in reality, none of the choices is worse than another. Why is it?

The value of a choice lies in the difference

Satohiro Tajima, a researcher in the Department of Fundamental Neuroscience of UNIGE's Faculty of Medicine, has devised a simple mathematical model that demonstrates the following: The optimal strategy for two propositions is to summarize the values ​​associated with the memories that you have each choice. , then calculate the difference between these two sums (do I have more positive memories related to chocolate or macaroons eclairs?). The decision is made when this difference reaches a threshold value, set in advance, which determines the time taken to make the decision. This model leads to rapid decision-making when the values ​​of the two possibilities are very far apart. But when two choices have almost the same value, we need more time, because we have to use more memories for this difference to reach the decision threshold. Is the same process at work when we have to choose between three or more possibilities?

The average of the values ​​for each choice determines the winner

For each choice, we want to maximize the possible gain in a minimum of time. So, how do we proceed? "The first step is identical to that of a binary choice: we accumulate memories for each choice in order to estimate their combined value," explains Alexandre Pouget, professor in the department of fundamental neuroscience of UNIGE. Then, using a mathematical model based on optimal stochastic control theory, instead of looking at the cumulative value associated with each choice independently, the decision is based on the difference between the cumulative value of each choice and the average value of the accumulated values. all the choices. As in the previous case, the decision is made when one of these differences reaches a predetermined threshold. "The fact that the decision is based on the cumulative value minus the average of the values ​​of all the possibilities explains why the choices are inconvenient, even when some differences are glaring," continues Professor Pouget.

If the different possible choices have similar values, the average will be almost identical to the value of each choice, which will lead to a very long decision-making time. "Making a simple choice can take 300 milliseconds but a complicated choice sometimes lasts a lifetime," notes the Geneva-based researcher.

The study of UNIGE shows that the brain does not make decisions based on the value of each opportunity, but according to the difference between them. "This underlines the importance of the feeling of having to maximize the possible gains that can be achieved," says Professor Pouget. Neuroscientists will now focus on how the brain revisits memory to appeal to the memories associated with each possible choice, and on how it simulates information in the face of the unknown and when it can not. not make a decision based on the briefs.