[anorakoverflow]

You raise some points that were also raised by a sibling commenter, but I’ll try to reply to them. You are correct that FB and EC are different concepts that are unfortunately often used interchangeably (even in research). This stems from the fact that there was no robust definition offered when the concept was introduced. Bruns offers a definition to distinguish the concepts.

> The former is passive, and you have no choice. The latter is human nature. Birds of a feather and such.

Both concepts are closely related to the idea of homophily, the preference to connect or communicate with like-minded individuals (birds of a feather, as you say). In Bruns’ definition, echo chambers mean the preference to connect, while filter bubbles mean the preference to communicate. Both of them are, as you say, human nature at their core. The concepts go further than homophily, though, in that they also exclude individuals or information outside of the chamber or bubble.

> "Appear to encounter" is a vague.

This is from the research abstract summarising recent empirical findings. I think some critical distance is warranted.

> Thst aside, encounter doesn't mean you're open to those ideas. (…) The exposure doesn't open their mind, it backfires and pulls the blinders even more narrow. I missed where this study addresses that boomerang effect.

This effect is addressed as a “oppositional reading stance” in the section “Social and Political Relevance and Impact”.

> Again, "exposure" isn't necessarily leading to more diverse ideas.

You are correct. However, if individuals are encountering information contrary to their bubble’s or chamber’s belief, we would have to conclude that there is no FB or EC at work as it has failed to exclude this information. If the bubble or chamber was as robust as claimed by Pariser and others, this content would not have reached the individual.

> From multiple sources I've read that limited ownership is leading to consolidation.

You are referring to ownership structures. “Fragmentation of national mediaspheres” here refers to the audience, specifically the concern that the increasing number of media offers, especially with the advent of the internet, would fragment the national audience and have adverse effects on discourse and democracy.

> That might be true, but it's not proof that FB or EC don't exist.

It is not epistemologically possible to prove that these effects do not exist. There is limited evidence that they exist in specific contexts, but barely any evidence for a population-wide effect.