  Nowadays users get informed and shape their opinion through social media.
However, the disintermediated access to contents does not guarantee quality of
information. Selective exposure and confirmation bias, indeed, have been shown
to play a pivotal role in content consumption and information spreading. Users
tend to select information adhering (and reinforcing) their worldview and to
ignore dissenting information. This pattern elicits the formation of polarized
groups -- i.e., echo chambers -- where the interaction with like-minded people
might even reinforce polarization. In this work we address news consumption
around Brexit in UK on Facebook. In particular, we perform a massive analysis
on more than 1 Million users interacting with Brexit related posts from the
main news providers between January and July 2016. We show that consumption
patterns elicit the emergence of two distinct communities of news outlets.
Furthermore, to better characterize inner group dynamics, we introduce a new
technique which combines automatic topic extraction and sentiment analysis. We
compare how the same topics are presented on posts and the related emotional
response on comments finding significant differences in both echo chambers and
that polarization influences the perception of topics. Our results provide
important insights about the determinants of polarization and evolution of core
narratives on online debating.
