I've alsways assumed that, like me, most Americans can tell the difference between broadly English, Scottish, and Irish accents.

Undoubtedly movies and other media helped my education, along with having grown up in a big city where there were many Irish and not a few Scottish and English immigrants.

A hundred years ago, I'll bet few Americans outside of such cities could have distinguished such accents, unless they'd paid close attention to the clumsy representations in novels and newspapers. The Irish in those sources always said "Oi" for "I" and stuff like "t'ing" and "murther," and words like "river" often had extra r's attched ("river-r-r") to indicate Scottishness.

Cornish and other English accents that retain more r's than, say, in London, probably sound "Irish" to most Americans. My guess is that Americans can distinguish between the stereotypical cockney and Beeb accents, again because of the media. But how can anyone know? (My experience has been largely among academics who are keen on this sort of thing.)

Probably fewer Americans can recognize a Canadian than an Australian accent, partly because Canadian accents - outside of the Maritimes - aren't all that distinctive. Most Canadians sound pretty much like American Northerners.

Many Americans, especially from the West, believe they have "no accent," and many others believe them. But everybody has an accent, though some are less obvious than others.

Even my Tennessee friend was once told by a woman in London that he had a "very American accent," but she couldn't identify it more precisely than that. Here in the U.S., it stands out.