Slips of the lip stay all in the family: Dogs included, but not the cat

Among people who know each other well, the wrong name is usually plucked from the same relationship category, the study finds. Friends call each other by other friends' names, and family members by other family members' names. And that includes the family dog.

"It's a cognitive mistake we make, which reveals something about who we consider to be in our group," said Duke psychology and neuroscience professor David Rubin, one of the study authors. "It's not just random."

The new paper, based on five separate surveys of more than 1,700 respondents, appears online this week in the journal Memory and Cognition.

Many of the patterns didn't surprise lead author Samantha Deffler, a Ph.D. student at Duke. One did, though.

In addition to mixing up sibling for sibling and daughter for son, study participants frequently called other family members by the name of the family pet -- but only when the pet was a dog. Owners of cats or other pets didn't commit such slips of the tongue.

Deffler says she was surprised how consistent that finding was, and how often it happened.

"I'll preface this by saying I have cats and I love them," Deffler says. "But our study does seem to add to evidence about the special relationship between people and dogs.

"Also, dogs will respond to their names much more than cats, so those names are used more often. Perhaps because of that, the dog's name seems to become more integrated with people's conceptions of their families."

Phonetic similarity between names helps fuel mix-ups too, the authors found. Names with the same beginning or ending sounds, such as Michael and Mitchell or Joey and Mikey, were more likely to be swapped. So were names that shared phonemes, or sounds, such as John and Bob, which share the same vowel sound.

Physical similarities between people, on the other hand, played little to no role. For instance, parents were inclined to swap their children's names even when the children looked nothing alike and were different genders. It's not a question of aging, either: The authors found plenty of instances of misnaming among college undergraduates.

Although misnaming is a common theme in popular culture, Deffler said the new study is one of few describing how the phenomenon works.

Deffler is no stranger to the experience in her own life. Her graduate supervisor frequently swaps the names of his two graduate assistants. And growing up, she said, her mom often called her Rebecca, Jesse or Molly -- the names of her sister, brother and the family pit bull.

"I'm graduating in two weeks and my siblings will all be there," Deffler said. "I know my mom will make mistakes."

Now she knows why.

In addition to Deffler and Rubin, the authors included Duke postdoctoral researcher Christin Ogle and Cassidy Fox, a 2013 Duke graduate. Fox helped lead the research project while studying at Duke as an undergraduate and devoted her senior thesis to the topic.