When our prejudices bias our decisions

Research Mis en ligne le 8 mars 2017
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When we face two mutually exclusive options, our brain starts with assigning a value to each in order to compare them. Mathias Pessiglione’s team at the ICM looked at our brain’s mechanisms in dealing with such situations. The results were recently published in eLife.

What would you rather listen to, Céline Dion or Keith Jarrett? When you make this choice, your brain assigns a value to each option. A small area, the ventromedial prefrontal cortex (vmPFC), then compares these two values and calculates their difference. The information is then relayed to the other regions of the brain that trigger the action required by this choice, and you listen to Céline Dion!

But what exactly do we compare and what mechanisms are involved? The hypothesis of Mathias Pessiglione team is that our decision-making is biased and determined by our preferences a priori. Their goal is to determine if and how the vmPFC uses these existing preferences – pop rather than jazz – to make a decision.

The researchers conducted a study in which volunteers had first to evaluate a number of artists belonging to different musical genres. Then, the participants, whose cerebral activity was recorded by functional MRI, had to choose the one that he/she preferred between two of these artists.

To make this choice, the volunteers take into account two parameters: the kind of music, I prefer jazz or pop, and the artist presented; a pop fan could for example choose jazz if the option for pop is Britney Spears.

The researchers showed that the subjects’ decisions were influenced by their a priori preferences. Pop fans choose Britney Spears or Celine Dion more often than expected by their individual evaluation of the artists. Indeed, pop fans will choose « by default » pop artists if the other alternative is from a different category, jazz for example. This “default” choice is explained by a higher basal activity of the vmPFC when an option from the “a priori preferred” category is presented to the volunteer. The vmPFC reports the value difference to the benefit of the a priori preferred option, so the stronger its activity, the more the person tends to choose the “default” / a priori preferred option.

Similar results were obtained when the proposed choice was about food (sweet or salty?) or reading (fashion or sports magazine?).

The brain thus uses a general strategy for decision-making that saves time and effort, but introduces biases.
Mathias Pessiglione’s team now wants to understand how the downstream regions of the brain use vmPFC’s signals to choose the preferred option.

Reference : How prior preferences determine decision-making frames and biases in the human brain. Lopez-Persem A, Domenech P, Pessiglione M. Elife. 2016.