When we're with others, most of us "self-monitor." That is, we try to please the people around us by adapting our behavior to suit theirs.
But when we're with an intimate partner, we often let go of this pattern of behavior and instead "talk fluidly and naturally," Shenk writes.
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In addition to having their own private vocabulary, long-term couples eventually "start to match each other in the basic rhythms and syntactical structures of their speech," writes Shenk.
Part of that is a result of a phenomenon that psychologists call "emotional contagion." Basically, when two people spend enough time together, they begin to match each other's speech patterns.
In other words, we stop having to constantly check ourselves before we speak. Many of the pairs Shenk talks to in his book have such a relationship.
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I love your columns about long distance relationships, and had a question of my own: in an LDR, who should be the one to move?
We mimic everything from the other person's accent to the amount and length of pauses he or she puts between words and sentences.
There's some evidence to suggest that these changing speech patterns can even serve as one indicator of how long a couple might stay together.