FOREIGN ACCENT SYNDROME

People keep waking up from head injuries speaking a different language? (...) The syndrome is caused by damage to the part of the brain that controls the muscles used to produce speech.
"Speaking requires very precise control of the muscles of lips, tongue, and jaw (the speech articulators) and the larynx (voicebox)," wrote Lyndsey Nickels from Macquarie University for the Conversation back in 2013.

What is foreign accent syndrome?
This phenomenon is known as foreign accent syndrome, a rare disorder that usually arises after brain damage as a result of, for example, stroke or head injury.
(...) What causes foreign accent syndrome?

Foreign accent syndrome is caused by brain damage which impairs the control of the muscles used to produce speech.

Speaking requires very precise control of the muscles of lips, tongue and jaw (the speech articulators) and the larynx (voicebox). If the placement of the articulators, speed or coordination of movements are slightly out of sync, then speech sounds will be altered. For example, when people are drunk the effects of alcohol on muscle control and coordination causes distortion of the speech sounds and leads to the perception of slurring.

Vowels are particularly susceptible: which vowel you say depends on where your tongue is in your mouth. Slight differences in where your tongue is – how far forward or back, how high or low in your mouth – changes the vowel you produce. Different languages have different vowels and within a language one of the main differences between accents is in the vowels. Aussies accuse Kiwis of saying “fush and chups” and Kiwis of Aussies “feesh and cheeps”!

Research has shown people with foreign accent syndrome nearly always have trouble producing vowels. Brain damage affects their ability to control their tongue movements. There may be too much or too little muscle tension and therefore they may “undershoot” or “overshoot” their target. This leads to the vowels sounding different, and sometimes they may sound like a different accent.

Another commonly reported feature of foreign accent syndrome is a problem with the stress pattern of words and rhythm and intonation of sentences (prosody). People with foreign accent syndrome may speak slowly, separate out syllables and say each one with equal stress – for example, “banana” as “bar-nar-nar” rather than “buhNARnuh”.

So, the problems with muscle movement and coordination cause in changes to the way the speech sounds. When the new speech sounds are similar to those of an existing accent, the speaker can be perceived to be speaking with a foreign accent. People with foreign accent syndrome don’t speak with all the features of a foreign accent, but there are enough things about the way they speak to make it seem as though  they have a different accent.