  Social media platforms attempting to curb abuse and misinformation have been
accused of political bias. We deploy neutral social bots who start following
different news sources on Twitter, and track them to probe distinct biases
emerging from platform mechanisms versus user interactions. We find no strong
or consistent evidence of political bias in the news feed. Despite this, the
news and information to which U.S. Twitter users are exposed depend strongly on
the political leaning of their early connections. The interactions of
conservative accounts are skewed toward the right, whereas liberal accounts are
exposed to moderate content shifting their experience toward the political
center. Partisan accounts, especially conservative ones, tend to receive more
followers and follow more automated accounts. Conservative accounts also find
themselves in denser communities and are exposed to more low-credibility
content.
