@Mitch You mean it's about auditory phonetics and not articulatory phonetics?

@Mitch There's a continuum between Broad Scots and Scottish Standard English. When I talk to people in Scotland, which I do on pretty much a daily basis, I can usually understand everything they say just fine, but that's because they're staying toward the Standard English end of the spectrum. I don't speak Scots at all.

In his Dictionary of Linguistics and Phonetics, David Crystal defines accent as "The cumulative auditory effect of those features of pronun-ciation which identify where a person is from, regionally or socially."

Humans are actually really good at understanding different accents, but there's a period of adjustment. When you first hear an unfamiliar accent, it can be difficult, but the next day it should be a lot easier, and after a week it should be no problem at all. But when it comes to dialects ("A regionally or socially distinctive variety of language, identified by a particular set of words and grammatical structures.") or entirely different languages like Scots, that's another story.

The biggest difference between accents is usually in the vowels, and our brains have a way of adapting to those differences relatively quickly. The consonants can be a bit trickier to adapt to, but the differences there usually aren't as big.

Differences in intonation are, unfortunately, still understudied and poorly described at this point.

@tchrist That's actually a really good point. The (subjective, not actual) isochrony of Indian English makes things a bit difficult for me as an American English speaker.