I had a friend who was born in the UK and lived in the States from the ages of 4-9, lived in England until he was 18 and then moved to the States. His accent was neither here nor there. He sounded neither British nor American. If he drank, he sounded more English, but otherwise he sounded in betweenish. He could do a perfect mid west accent on occasion.
My mother was born and raised in England, and came to the U.S. at the age of about 19 or 20 (she’s in her 70’s now). She went from London to West Virginia, and now has a rather strange accent as a result. Most people guess she’s Australian.
On one visit to the UK, my own voice was starting to sound strange to me toward the end- I’d say something, and be surprised not to hear a British accent. I think I would have picked it up at least partially if I’d stayed.
I don’t think I’d have picked it up completely, though- I don’t fully pick up accents (people always think I’m from somewhere else, even where I grew up they thought that). I suspect it’s connected to the fact that I don’t really notice hear tone of voice most of the time, plus I’m very tone-deaf when it comes to music.
I’m not sure even a normal person who can hear accents better than I can could do it, though. When I was an undergrad, I was a TA for a non-major physics class on the physics of sound and music. The professor said that humans are born able to make and distinguish between lots of different sounds, but that ability goes away after you learn your native language- you lose the ability to differentiate between sounds that aren’t considered different in your language. I was taking a class with a TA who was a native speaker of Russian, and I arranged for my TA to come in to the sound-and-music class on the day the professor brought in a voice spectrum analyzer. My TA pronounced two sounds that sounded alike to me and the rest of the class, but showed up differently on the voice spectrum analyzer- there are sounds that Russian-speakers differentiate between that I, as a native English speaker, can’t. I suspect this effect would be less extreme for languages or dialects that were more closely related (like British and American English), but it would presumably still be there.
I don’t think is quite as hard and fast as you think it is. My father moved to the US from the UK when he was 17. He now speaks with a slight New Jersey accent, but there are -no- traces of a British accent, aside from an occasional odd word choice (referring the sidewalk as the pavement being one of them). Even with these British word choices, however, he still uses American vowel sounds and stresses.
For what it’s worth, he did make a conscious effort to lose his English accent when he joined the USAF.
At 18 my mum moved from Ireland to Yorkshire with her 16 year old sister and mum. This was the 70s and because of the racism she changed her accent as soon as she was able to.
My mum and aunty now both have Yorkshire accents. Oddly, my mum can not now even fake an Irish accent. My Grandma however still has a very Irish accent.
Peter Jennings picked up a bit of an accent in London when he was the foreign correspondent for ABC Nightly News, before he got the anchor chair.
Slithy Tove writes:
> So would would Madonna’s likelehood of acquiring a legitimate English accent
> be accelerated or hindered by the one she deliberately affected the day she got
> off the plane?
Madonna’s accent is far weirder than that. She started speaking that way several years before she moved to the U.K. It has never sounded like a real British accent. It sounds like she has been taking elocution lessons from an insane elocutionist. Nobody understands where that accent came from.
It’s hard to make any kind of generalization. My grandparents, who came to the U.S. in their early 20s, were still speaking with thick, native accents 70 years later. My father, who grew up in Chicago, lost his accent completely when we moved to Texas (he didbn’t sound like either a Texan or a Chicagoan), but regained it when he moved back to Chicago. When I lived a mere 175 miles from here, my friends from up here thought I sounded like I was from down there, while my friends down there thought I sounded like I was from up here. And my adult children sound like they were born and raised here (which they were), while my wife and I don’t.
Hell, it can differ from New Jersey to Pennsylvania; I recall at some point in college trying to illustrate to Pennsylvania friends the difference between north New Jersey pronunciations of “Mary” and “Marry”, and they just could not hear it. I was surprised, they were surprised, it was all in all quite surprising.
Seriously…that one’s always puzzled me (I’m from Altoona, PA). I can’t distinguish Mary, marry and merry at all. We say them all exactly the same as far as I can tell.
Likewise in Cleveland, Ohio. But I know longtime New Englanders who say each slightly differently.
Here’s the gist of it:
We say “Mary” about the same way you probably say all three. [This would actually be the trickiest one to describe. We might think of this as the vowel in “bait”, but it’s actually a diphthong which starts with the vowel in “bet” and then centralizes]
We say “Marry” using the vowel in “bat”.
We say “Merry” using the vowel in “bet”.
Well, I suppose, depending on where you’re from, the way you say all three might be more like the way we say “merry” (with the vowel in “bet”, straight-up). At any rate, I’m no expert, but that’s my understanding of the situation.
But why, given the choice, go Canadian? Here he was, making a new start, and he defaulted to a bland CBC-Toronto? 
My own accent varies by who I’m talking to. A 1950-60s childhood in Minnesota, Chicago, and Virginia left me with not knowing what I sound like, and as late as the 80s people could not place my “normal” accent. I think it is now Pretentious Midwesterner, but when I’m down south it starts heading into Pretentious Virginian, and NOBODY is as pretentious as Virginians. 
What surprises me is how much the accents of Europeans have changed since WWII. At the bus station Mom and Pop, who had moved to Rockford, IL, in the early 50s, met their kids fresh over from the Old Country. Dad and Mom sounded like Ole and Lena while the kids sounded like Generic Western Europeans–and this was 35 years ago. I used to speak some German but the modern accents and vocabulary have me flummoxed but I saw a movie set in 1920, when my teacher would’ve been a kid, a while back in which the female lead HAD to be from Dusseldorf like my teacher because she was the first German person I’d understood in years, but she was from LA and had apparently studied under someone who REALLY knew their German accents from before WWII. Modern Europeans? Hell, I can’t place their COUNTRIES, much less their cities.
Fifty-four posts and nobody has mentioned the archetypal transatlantic accent, Loyd Grossman? (YouTube link)
That sound is apparently what you get when you take a Boston accent and transplant it to the UK for 30-odd years.
He’s the archetype? Not Cary Grant or Alistair Cooke?
The poor woman!
Did it stop at just the accent?(Though thats bad enough)or did she start wiping her nose on her sleeve,looking for things to eat in dustbins and asking people from southern England if they had any spare change?
Yeah, people from the Manchester area sure are such filthy beggars. And the one good thing about the way they speak is that it lets us identify them upfront…
I had a similar experience with those silly Western Pennsylvanians and their bizarre belief that the names “Don” and “Dawn” sound the same.
Oh Og. Don’t get me started on Newcastle. I want to punch them in the face when they start talking and kick them out of my shop.
I just feel sorry for Mancs, and I’ll let them in my shop so long as they keep their shirts on.