How your facial muscles reveal what you really think. 'It only works on people who haven't had Botox.'

14 November 2025 Research news item

Do you ever have doubts about what someone says to you, but think you are good at hiding your judgment? Your facial muscles betray more than you think, even if it is not always visible to the naked eye. With the help of technology, philosopher Harriet Yates measures subtle movements of facial muscles to detect implicit judgments, for example when we look at hate speech.

When interacting with others, we usually assume that the other person is committed to what they say. Philosophers find such commitments very interesting. This is a different kind of commitment than that in a relationship or dedication to a particular goal. Commitments in conversations are about committing to the truth of what you say.

To better understand what exactly happens and how commitment works, Harriet Yates and the team she works with, led by Corien Bary, are using a new method. They measure the activity of facial muscles in test subjects as they read stories.

Yates: "If I say, ‘Tom is a vegetarian,’ I am committing myself to the truth of what I am saying. If you then hear me say, ‘Tom eats a lot of tofu,’ that fits in with what I said earlier, and as a listener, you will not be surprised. But if I say instead, ‘Tom eats a lot of meat’, you will be surprised, or perhaps even indignant. As the speaker, I have violated my earlier commitment. At that moment, as a listener, you tense your facial muscles in a way that allows us to deduce that you are surprised or indignant.'

Deep frown

Sometimes you can tell from someone's furrowed brow that they have a certain opinion or don't understand something. But not every frown is visible to the naked eye. Using facial electromyography (fEMG), Yates can measure that frown: the more the frown muscles are activated, the stronger the surprise or indignation. By measuring facial muscle activity, the researcher knows how test subjects interpret certain conversations in the experiments. But, she says, “the method only works on people who haven't had Botox injections.”

“The potential applications of this method are numerous,” the philosopher continues. For example, this research could offer a solution to miscommunication, such as in cases of undesirable behavior. "With this method, we can measure invisible tension in facial muscles. This shows when someone hears, reads, or sees something that does not match their expectations. If fEMG can demonstrate that ‘most’ people would react negatively to a particular statement made by a speaker, then the speaker has apparently committed themselves to something that led to different expectations. The speaker can then be held more accountable for what they say."

Armchair philosophy

In early April, Yates received a Mohrmann Stipendium: a grant for female PhD students, intended to further their doctoral research. With this grant, the researcher will attend conferences to share the results of her research. In addition, she hopes to organize a Commitments in Conversation workshop at Radboud University for researchers in the field of commitment, in order to stimulate an interdisciplinary discussion on this topic.

“For hundreds of years, philosophy was mainly practiced from armchairs: sitting and thinking. Now we can use other, more experimental scientific methods to develop new theories,” says Yates. She wants to apply the method to people who watch hate speech videos, for example. "This allows us to see how the presentation of slurs—a direct slur, saying ‘so-called,’ or putting the slur in quotation marks—can influence how the other conversation partner can hold the speaker accountable. It is already quite remarkable that we now know that fEMG can give us new information about what happens when people hear or read stories. Anything else we can investigate with this method is pure bonus."

Photo via Unsplash

Contact information

Organizational unit: Faculty of Philosophy, Theology and Religious Studies
Theme: Philosophy, Behaviour