In Western-style democracies, ideological polarisation, thought of as the difference in attitudes between supporters of different ideological groups is on the rise. Nevertheless, political conflicts more often reflect social-identity divisions rather than ideological differences. This leads to affective polarisation, reflected in positive affective attitudes towards ideological ingroups and negative attitudes towards outgroups. Since research usually treats both phenomena separately, which hinders understanding of the mechanisms of their (mutual) influence, I examined the interplay of affective and ideological polarisation in the formation of intentions for civic participation. 610 participants aged between 18 and 90 (M = 40.86, SD = 16.61, 69% left-wing, 27% right-wing supporters) took part in the online survey, which included a series of questionnaires and an experiment. Based on the questionnaires results, I conclude that participants overestimate the extent of actual polarisation between the two ideological groups (left- and right-wing supporters) in their support for different socio-political measures. The level of actual polarisation is most overestimated by older individuals and those perceiving their ingroups and outgroups as more affectively polarised. In an online experiment, participants were exposed to civic participation cues of either their ideological ingroup or outgroup. Results show that affective polarisation increases with exposure to civic participation cues of both groups, and psychological reactance increases with exposure to participation cues of the outgroup. Using mediation analysis I showed that psychological reactance can explain the psychological mechanism of affective polarisation. Participants thus interpret the activity of the outgroup as a threat to their independent decision-making, which increases affective polarisation. I have also developed a model showing that psychological reactance moderates the relationship between perceived ideological polarisation and intention for civic participation. This implies that affective responses to outgroup participation cues in the form of psychological reactance can activate perceived ideological differences and thereby foster intentions for civic participation. This thesis shows that affective polarisation is a dynamic phenomenon that varies according to social situations and identifies some psychological mechanisms of affective polarisation.
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