This dissertation seeks to improve our understanding of the process by which citizens' selective exposure contributes to attitudinal polarization and engagement in political activities. In this dissertation, I test two models that explicate the relationship between selective exposure and political polarization and participation. The knowledge model suggests that the effects of selective exposure on individuals' attitudinal polarization and political engagement are mediated by knowledge of candidate issue stances. The stereotype model proposes that selective exposure indirectly influences polarized attitudes and political participation via stereotypical perceptions of candidates (i.e., McCain's age and the prospect of a Black presidency). By posing issue knowledge and stereotypical perceptions as potential mediators, this study extends current literature to analyze why and how selective exposure leads to polarization and political participation. The results provide evidence that selective exposure influences individuals' stereotypical perceptions of the candidates' age and race, and these stereotypic perceptions influence attitudinal polarization and participation in campaign activities. There was no support for the knowledge model; selective exposure did not have a significant relationship with citizens' issue knowledge nor did it play a mediating role in the relationship between selective exposure and political polarization and participation. This dissertation thus challenges the argument that selective exposure is normatively desirable due to its contribution to citizens' greater levels of political participation. The findings of this study call into question such a contention because the results show that individuals who engage in selective exposure are motivated to participate in political activities by forming stereotypic perceptions of candidates rather than by gaining factual issue knowledge, which is in contrast to democratic theories' assumptions of informed citizenship. Turning to the role of exposure to dissonant media outlets, two contrasting roles were found. On one hand, results offer some evidence that dissonant media use contributes to gaining issue knowledge and inspiring citizen participation. On the other hand, some findings suggest that it reinforces, rather than attenuates, citizens' attitudinal polarization and stereotypical perceptions of candidates. Thus the findings from this study offer mixed support for encouraging citizen exposure to dissimilar viewpoints. / text

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