Brain waves show your bias before you make a choice


The strength of alpha brain waves reveals if you are about to make a biased decision, according to research recently published in Journal of Neuroscience.

Everyone has bias, and neuroscientists can see what happens inside your brain as you succumb to it.

The clue comes from alpha brain waves – a pattern of activity when the neurons in the front of your brain fire in rhythm together. Alpha brain waves pop up when people make decisions, but it remains unclear what their role is.

This is a diagram from the study
The strength of alpha brain waves (left) reveals biased decisions (right). The image is credited to Grabot and Kayser, JNeurosci 2020.

Grabot and Kayser used electroencephalography to monitor the brain activity of adults while they made a decision.

The participants saw a picture and heard a sound milliseconds apart and then decided which one came first. Prior to the experiment, the researchers determined if the participants possessed a bias for choosing the picture or sound.

Before the first stimulus appeared, the strength of the alpha waves revealed how the participants would decide. Weaker alpha waves meant resisting the bias; stronger alpha waves indicated succumbing to the bias.

What Is Bias?

A bias is a tendency, inclination, or prejudice toward or against something or someone. Some biases are positive and helpful – like choosing to only eat foods that are considered healthy or staying away from someone who has knowingly caused harm.

But biases are often based on stereotypes, rather than actual knowledge of an individual or circumstance. Whether positive or negative, such cognitive shortcuts can result in prejudgments that lead to rash decisions or discriminatory practices.

Bias is often characterized as stereotypes about people based on the group to which they belong and/or based on an immutable physical characteristic they possess, such as their sexuality.

This type of bias can have harmful real-world outcomes. People may or may not be aware that they hold these biases.

The phenomenon of implicit bias refers to societal input that escape conscious detection. Paying attention to helpful biases – while keeping negative, prejudicial, or accidental biases in check – requires a delicate balance between self-protection and empathy for others.


Alpha waves, in general, occur when neurons in the forefront of the brain fire in tandem with one another (they’re often pulsing through our brain during relaxed, awake states, like meditation).

Past work suggested that alpha waves are related to how we perceive the world — they affect visual and audio perception, for instance. That led to the idea that they’re involved with whether we’re seeing reality for what it actually is.

However, Grabot explains that her work suggests that alpha waves are more ATTUNED TO OUR BIASES about the world, rather than simply reacting to how things actually are.

“We show in our work that alpha waves are not predicting how correct our perception will be, but more whether we will follow, or not, our internal biases, independently of the response’s accuracy,” she explains.

The team examined how brain frequencies responded to bias stimuli. Laetitia Grabot, Christoph Kayser

To examine how alpha waves affect our perceptions, Grabot and her team asked 24 people to look at pictures and listen to a series of tones, which were staggered by a nearly imperceptible distance of 20 to 250 milliseconds.

Then, the participants had to guess which came first – a tone or a picture.

Those who consistently saw the pictures first (even if they weren’t actually presented first) were grouped as biased towards images. Those who saw sounds were biased towards audio.

The whole time, the team took images of their brains to analyze how alpha waves behaved during that process.

Ultimately, they found that the strength of alpha waves before the picture or sound was presented affected how the person reacted. Strong alpha waves before the stimulus were correlated with succumbing to bias. Weaker alpha waves were linked to resisting it.

Source: SfN


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