LOCAL accents in almost all main North American cities are diverging at an unprecedented rate and new dialects are emerging among white English-speakers, according to linguists.
The changes, very often in vowels, make it increasingly difficult for white Americans from one city to understand isolated words or names from another.
William Labov, professor of linguistics at the University of Pennsylvania, told the association that up to 40 per cent of Philadelphia's white population do not understand isolated words when an advanced form of the Chicago dialect - the Northern cities shift - was played to them.
"American dialects are getting further apart," said Professor Labov, who has completed the first map of white American dialects. "Despite the influence of radio and television, on which such modern dialects are not heard, at least at first, all the great cities are moving some way towards new sound patterns without realising it."
The shift, Professor Labov claims, has taken place over 50 years. "Why it happens is still a mystery," he said. "We know that the leaders are normally women. We think that they don't know they are doing it. By the time they are aware, the change is over."
But this regionalisation is not seen among African-Americans, Professor Labov said. "Plenty of people of African-American descent sound like whites. But they speak standard English, not with the local accent. This is a difference with England where West Indians and Pakistanis adopt the local form of speech."
Professor Labov said this may be a result of traditional separation. "There is no residential segregation in the UK similar to the US," he said.