181 EXTENDED ABSTRACT Political communication in heterogeneous lifeworlds. Communicative practices of political milieus and conditions for their integration Raphael Kösters & Olaf Jandura “Stratamentation” as a challenge to the public sphere’s function of integration Our study uses the public sphere’s function of integration (Imhof, 2011) as a starting point: By providing audiences with a common basis of issues and knowl- edge, the public sphere of the mass media establishes the basis for the self-percep- tion of a heterogeneous society as one social community. If issues are discussed in a pluralistic and discursive manner, mass media constitutes a shared perception of political reality and can even encourage the mutual tolerance of diverse view- points in society. In this way, public communication also serves as the basis for identity-building and for citizens’ political participation (political integration). More generally, shared issues and knowledge are necessary for basic modes of social communication. Apart from the democratic performance of the mass me- dia, we also need to look at a nation’s political culture and its citizenry’s heteroge- neity. The success of an integrative public sphere depends upon the willingness of politically and socially diverse groups to participate in public discussion and to be aware of and to accept others’ viewpoints. Research on audience fragmentation questions in which parts of society these requirements are still met. In fact, social heterogeneity is perceived as a challenge to an integrated public sphere as we fnd tendencies of “stratamentation” across the citizenry (Bennett & Iyengar, 2008; also see Imhof, 2013; Tewksbury & Rittenberg, 2012; van Aelst et al., 2017). Stratamentation involves two parallel processes: First, the citizenry is stratifed in terms of diverging degrees of political and media involvement (vertical dimen- sion). Based on this, certain social groups avoid news media altogether, or their exposure to political content remains rather incidental and infrequent (Lee, 2009; Mothes, 2017). Such groups might lack the substantial basis needed for opinion- building and expressing their political positions. Consequently, growing political knowledge gaps, as well as diverging degrees of political participation, are to be expected (e.g., Bächler & Bonfadelli, 2012). Second, those who are highly in- volved are segmented in terms of diverging belief systems (horizontal dimension). In such groups, specifc worldviews guide the selection and processing of media content (Knobloch-Westerwick, 2014; Yeo, Cacciatore, & Scheufele, 2015). In