Extreme ingroup and outgroup perspectives counter-intuitively impact intergroup polarisation at the level of neural oscillations

A powerful example of affective polarisation occurred between vaccine-supporters and -opposers when vaccinations were implemented to counter the recent global pandemic. In this social neuroscience study, we scanned 121 vaccine-supporters using magnetoencephalography to evaluate three levels of polarisation: explicit, implicit, and neural — and then to test whether exposing people to extreme ingroup perspectives (following the paradoxical thinking principles) or extreme outgroup perspectives can modulate those levels of affective polarisation between vaccinated and unvaccinated individuals. We show that a neural proxy for intergroup polarisation, expressed as late prefrontal beta rhythm suppression, can detect subtle changes in affective polarisation. More specifically, we find that exposing vaccine-supporters to extreme ingroup (i.e., pro-vaccination) viewpoints leads to a decrease in this neural proxy of affective polarisation. Conversely, exposure to extreme outgroup (i.e., anti-vaccination) narratives increases polarisation, which in turn predicts a decrease in positive affect towards vaccine opposers almost one year later. Altogether, the results show that although it may seem intuitive to expose people to counter-arguments (i.e., extreme outgroup perspectives) to change their opinions, such an approach can backlash and increase polarisation instead. However, using subtler methods such as the paradoxical thinking intervention (i.e., extreme ingroup perspectives) for attitude change can have the desired effects and reduce intergroup polarisation.