By Stephanie Pappas, Senior Writer
Published: 02/05/2014 02:27 PM EST on LiveScience
Toddlers who don't talk much may not necessarily have a language delay, new research finds. Shy kids understand words, but when spoken to, they may clam up instead of speaking up.
The study is a step toward unraveling the question of why temperamentally shy children seem to develop language more slowly than other toddlers. Delayed speech is linked to social struggles later in life, so researchers wanted to understand whether shy kids can't produce language or simply don't want to.
The good news is that shy kids don't show language acquisition delays, said study researcher Soo Rhee, a psychologist at the University of Colorado, Boulder.
"The shyness is simply inhibiting the children from interacting with the experimenters and showing that they indeed have language abilities," Rhee told Live Science.[10 Scientific Tips for Raising Happy Kids]
About 15 percent of 12- to 24-month olds have shy temperaments. These kids exhibit what's known as "behavioral inhibition." They are bashful around other people and shrink away from new experiences.
Shyness is part of the normal range of human personalities, but numerous studies have linked a shy attitude to language delays in kids. In some cases, shy kids struggle with peer relationships and anxiety and depression later in life.
Scientists had floated a number of theories to explain why shy toddlers speak less adeptly than their more outgoing peers. Perhaps these children avoid interaction, so they get less practice speaking. Or the language struggles may come first, making children reluctant to interact with others. Another theory held that shy children aren't delayed at all; rather, extroverts are ahead of the curve.
Finally, some studies hinted that shy toddlers aren't really delayed — they "know it, but won't say it," Rhee and her colleagues write in an upcoming issue of the journal Child Development.
To test these ideas, the researchers recruited 408 families with same-sex twins in Boulder County, Colo. They conducted home visits and had the children come into the psychology laboratory at 14 months of age, 20 months and 24 months.
At these visits, the researchers assessed each child's temperament by observing how much they cried, clung to their parent or exhibited self-soothing behaviors such as thumb-sucking. They also tested language development by asking each child to imitate sounds, ask for help and follow directions. These tests determined how much language a child could produce, and separately, how much he or she could understand.
The shy children did show delays in their spoken language compared with more outgoing kids, the researchers found. But there was no such link between temperament and receptive language, or how much language a child understands.
Furthermore, the lack of speaking wasn't related to any actual language impediment. The researchers looked at the growth in language skills over time relative to each child's behavior. If they found that initial shyness led to initial language struggles and to less growth, it would suggest the kids weren't practicing speaking enough, explaining their deficits.
If, in contrast, the link between shyness and language showed up in expressive (spoken) language, but not in receptive (understood) language, it would support the notion that shy kids are functioning at the same language level but not displaying their talent. The latter was the case in this study.
And while delayed speech can be a sign of undiagnosed developmental problems, parents of shy kids may not need to worry. The researchers didn't look at brain development directly, but the patterns they found suggest there wasn't anything wrong with the shy participants physically or developmentally.
"One worry that we have is that shy children might just be underestimated in terms of their language abilities, so parents and teachers might not make as much of an effort to speak with them," Rhee said. "It seems perhaps that with children who are shy, one needs to make more of an effort to help children develop their expressive language abilities."