Language fluency is influenced by a number of factors such as age of acquisition and how often you interact with native speakers. However, in the case of sign language, a language “spoken” entirely using hand signs, researchers have identified another factor in fluency: handedness. The new study found that the speed at which sign language users understand other signers depends on whether the conversation partners are left or right-handed.

Researchers from the University of Birmingham in England found that, in general, British Sign Language (BSL) signers of both handedness respond faster to simple signs when watching a right-handed signers. This may be because right-handed signs are more common and seen more often. However, signers respond more quickly to complex two-handed signs when they are made by a conversation partner with the same handedness. This finding backs the idea of the spoken linguistic motor theory of speech perception, which states that people perceive spoken words in part by checking in with their own production system, also exists in non-spoken sign languages.

Read: Left-Handed People Have Ups And Downs, And Sometimes Rights: The (Possible) Dangers Of Being A Lefty

"Had all signers performed better to right-handed input, it would suggest that how signers produce their own signs is not important for understanding.” explained study so-author Dr. Robin Thompson, in a recent statement. “However, as left-handed signers are better at understanding fellow left-handers for two-handed signs, the findings suggest that how people produce their own signs plays a part in how quickly they can understand others' signing."

For the study, the UB researchers had 43 deaf fluent BSL signers of both handedness make judgements about signs produced by left of right handed sign models. They were shown a picture followed by sign, and asked if the two matched. The speed at which they responded accurately was then assessed.

At the moment, it’s not entirely clear why we develop preferences for different hands, or why lefties are the minority throughout the world. According to Scientific American, our handedness is believed to be influenced by both biological and genetic causes. For example, while the “D” gene is associated with right hand preference, the “C” gene determines handedness randomly, meaning that someone who inherits this gene has a 50/50 chance of being right handed or left handed.

This research is just further evidence that one’s handedness affects far more than which hand they write with. For example, in addition to sign language fluency, handedness can also affect your reading and comprehension fluency. According to a 2009 study, lefties are more likely to perform poorly in the ability to read, write, copy, and recognize symbols. For this reason, a higher number of lefties are diagnosed with dyslexia and attention-deficit hyperactivity disorder. This may be due to the fact that lefties tend to be right brain hemisphere dominant, where the left hemisphere of the brain is more closely associated with the majority of language processing.  

Source: Watkins F, Thompson RL. The relationship between sign production and sign comprehension: What handedness reveals. Cognition. 2017

See Also:

Why Is Left-Handedness So Rare?

International Left-Handers Day: What Are The Benefits Of Being Left-Handed?