Extract the answer to the question from the following context. Question: What allows you to know what dialect you are listening to? Context: Catalan is split in two major dialectal blocks: Eastern Catalan, and Western Catalan. The main difference lies in the treatment of unstressed a and e; which have merged to // in Eastern dialects, but which remain distinct as /a/ and /e/ in Western dialects. There are a few other differences in pronunciation, verbal morphology, and vocabulary.
The answer to this question is:
the treatment of unstressed a and e