Increasing perceived happiness in neutral faces by posing a smile: an EEG frequency-tagging study

Previous research using EEG has so far failed to provide strong and convincing evidence for the effects of facial feedback on the visual processing of emotional facial expressions. To fill this gap, we harnessed the power of EEG frequency tagging, which offers excellent objective indication of implicit stimulus processing with high signal to noise ratio. Healthy adult participants (N=47) from diverse backgrounds (tested in 2023/2024) viewed rare happy and angry oddball faces, interspersed with frequent neutral faces, while either producing a smile or keeping a neutral face. Smiling resulted in reduced neural discrimination of happy vs. neutral faces over the left occipito-temporal region, as shown by decreased power at the oddball frequency. These findings could reflect that voluntary smiling, and the associated change in facial feedback, leads to neutral faces being perceived as happier, providing evidence for the facial feedback hypothesis.