Background: I often notice that when I talk with someone with an accent that I often unconsciously start to imitate their accent. Similarly, you see some people that very quickly after moving to a country start to adopt the local accent whereas others maintain their original accent for many years.
TLDR When two speakers become more similar in their speech this is called convergence or accomodation (opposite: divergence). This can occur on all levels of language, phonetics and phonology, syntax, semantics, and pragmatics. When mutual intellgibility is not an issue, accomodation mainly occurs when speakers like each other or want to appear likeable.
Q: Has there been research on the process of unconsciously imitating accents?
Phonetic accommodation has been documented for a range of cases, for example for
Most studies have not studied spontaneous interaction and were mostly based on special elicitation techniques, but accommodation has also been documented in spontaneous speech (Levitan et al. 2012).
Q: What causes individual differences in the tendency to unconsciously take on accents?
We converge with interlocutors that we like or that we want to like us (shown by, for example, Babel 2009). We diverge from those that we don't like, although this may be rarer - In general, speakers adopt pronunciations that they think are socially desirable in a situation (see Mather 2012 and the classic study by William Labov it is based on).
I beg to disagree with @Skippy's opinion that people "without a firm sense of identity or an underdeveloped ego" are more likely to accomodate or converge with another speaker. It rather appears that converging with an interlocutor is a social skill connected to empathy. You speak more like your interlocutor or a group you interact with so that you will be accepted as one of the team. This will make social interaction and achieving your aims easier than if you did not accomodate.
I don't mean to say that there are not people with "a firm sense of identity" that are particularly unlikely to converge with other speakers. But I do disagree with the implication behind these phrases, namely that "a firm sense of identity" (and not accomodating) is something desirable and an "underdeveloped ego" (and accomodating) something undesirable. On the contrary, converging with other speakers is an important and valuable social skill that helps us connect with other people and establish common ground. Those who (even unconsciously) insist on not accomodating to other speakers could also be characterised as having problems in adapting to new people or groups they come in contact with and lacking in empathy.
But I do see the point that those who are desparate for the approval of other people might go to great lengths to get it - including accomdating their speech to a high degree.
I noticed that too. And it's not only the accent but the usage of words (different for lawyer and for a farmer), the sounds the person is making, movements and gestures.
I think it has something to do with "calibration" of your communication with your "opponent". to get the best possible results when the brain thinks it's possible.
Notice how you do the same with small children. I think it would be very weird if you try to talk with a toddler like: "Dear Mr. John Smith, I would like to ask you if you like this yellow toy made of plastic."
I am sure you would say something like "Johnny, do you like this yellow doggie?"
By calibrating I mean, that if you know the background, accent, social status you adapt, your brain makes some calculations and decide what is the most beneficial behaviour (yeah, selfish gene again ;) ) based on your experience etc.
In this case to make the communication the least problematic you try to sound and act a little like your opponent.
When you really don't like the person you will not sound like him. But be aware that if it's e.g. some guy that was popular in the school when you was younger you can pick his accent too ;). It's because even if you don't like him, parts of your brain sees him as somebody who was more successful, had more girls etc. and your body reacts to your hidden/deeper thoughts and memories and try to impress him by sounding/acting more like him.
Another important thing in this process is that sounding like the baby (high pitched voice), like a farmer/football fan (deep voice) transform you a little closer to your opponent. So you try to mirror him. And everybody is a little narcissist and like when he heard his voice (rewinding to your part on a record if you have a featuring as a singer) or see his own picture (the first thing after finding a picture is finding yourself) etc. ;)
Sometimes you imitate people when you don't like the person, but then it's intentional and not unconscious (as you mentioned in your question) and you try to make fun of or annoy that person etc.
I am adding this as an adjunct to @Derfder's answer.
I also emphasize, that, I will provide links, or references but my answer consists of my ideas and may, or may not have merit.
There is the idea that we mirror people we like, our body language will match. Even people's breathing rates can match when they are close.. and women's menstrual cycle's when cohabiting (as discussed here).. This could be a link with our mating and instincts as social animals.
So it follows, that our speech and/or accent can also change.
The albatross epitomises the art of mirroring, with their mating dance.
I also have a theory, that people, without a firm sense of identity, or an underdeveloped ego will be more likely to pick up accents of peoples around them. For example if they live in another country. Unlike their healthy adult counterparts, who generally keep their original accent, and it only changes gradually over time; they will be like children will pick up and accent of their environment, perhaps being delayed at the Conformist stage (E4)
The stages of ego development proposed by Jane Loevinger.
This link for the breathing and heart rates..followed by this link of publications Jan W. Kantelhardt.
Imitating others behavior patterns while speaking was found to relate more to a cognitive perspective taking than empathy.Chartrand and Bargh 1999
People who do adopt language patterns and accents are actually aware that this makes them fit it and more likable. However, this becomes more difficult to do with age. People who do not imitate accents/speech patterns easily may have a strong sense of identity with the region where they initially learned to speak.
On a personal note I have noticed a few young adults who have a diagnosed difficultly perceiving phonemes and have learned to lip-read to compensate for this are able to pick up accents more easily.
