Decision-Making: Bias Changes our Perception
EEG study examines the biased brain
When people face several choice options, external conditions can influence their decision-making and lead to bias. An experimental study at the Max Planck Institute for Human Development in Berlin has now shown that the brain processes visual stimuli more rapidly and comprehensively when biased toward a particular choice option. The study’s results have been published in the journal eLife.
Should you buy yourself a new car? It is generally thought that we consciously and unconsciously accumulate various sources of evidence for various choice options until a decision is reached. External conditions such as the current economic climate influence this decision process. If the economy is booming, we are more likely to go for a good deal on a new car. If the economy is poor, we may prefer to save our money, regardless of the new car’s allure. What is happening in our brain when such strategic biases influence our decisions?
A study led by Niels Kloosterman, research scientist in the Lifespan Neural Dynamics Group at the Max Planck Institute for Human Development, has now found a potential explanation. Using electroencephalography (EEG), the researchers measured the brain activity of 16 young adults while they were carrying out a decision-making task. Results indicated that the brain changes its “perceptual mode” as required by external conditions; the evidence in favor of what seems like a more advantageous decision are seen and collected far more rapidly than indications in favor of a seemingly more disadvantageous decision. This would mean that a good economic climate leads to our senses perceiving and accumulating cues in favor of a car purchase more rapidly than cues against it.
The researchers discovered this in experiments during which the participants saw random visual textures on a screen and had to press a button as soon as they recognized a rectangle within those textures. There were two experimental conditions that differentially influenced the participants’ decision-making. In the first condition, participants were penalized if they missed a rectangle; in the second condition, they were penalized if they pressed the button when the rectangle was not presented. As expected, the two conditions led to different response preferences. In the first condition, participants were more ‘liberal’ towards pressing the button, whereas they were more ‘conservative’ in the second condition.
Statistical analyses of participants‘ behavior and their EEG data showed that in the liberal condition, the participants’ visual cortex, the part of the brain involved in visual processing, was more active and more sensitive to stimuli. This change was not observed in the conservative condition. “If a certain decision promises to be more advantageous under certain external conditions, the ‘excitability’ level of our brain changes. The smallest indication of a rectangle was sufficient for our participants to press the button indicating they had seen it,” says Niels Kloosterman.
“By showing that decision biases influence the speed of information processing in the brain, we have been able to elucidate a key neural signature relevant for formal theories of decision-making,” states Douglas Garrett, co-senior author of the study and head of the Lifespan Neural Dynamics Group within the Max Planck UCL Centre for Computational Psychiatry and Ageing Research. Further examining this process during more complex decisions, such as deciding to purchase a car, will be one of the research challenges for the future.
Kloosterman, N. A., de Gee, J. W., Werkle-Bergner, M., Lindenberger, U., Garrett, D. D.*, & Fahrenfort, J. J.* (2019). Humans strategically shift decision bias by flexibly adjusting sensory evidence accumulation. eLife, 8: e37321. doi:10.7554/eLife.37321