Babies can say volume without saying a single word. They can wave good-bye, point at things to indicate an interest or shake their heads to mean "No". These gestures may be very simple, but they are a sign of things to come. Year-old toddlers who use more gestures tend to have more expansive vocabularies several years later. And this link between early gesturing and future linguistic ability may partially explain by children from poorer families tend to have smaller vocabularies than those from richer ones.
Vocabulary size tallies strongly with a child's academic success, so it's striking that the lexical gap between rich and poor appears when children are still toddlers and can continue throughout their school life. What is it about a family's socioeconomic status that so strongly affects their child's linguistic fate at such an early age?
Obviously, spoken words are a factor. Affluent parents tend to spend more time talking to their kids and use more complicated sentences with a wider range of words. But Meredith Rowe and Susan Goldin-Meadow from the University of Chicago found that actions count too.
Children gesture before they learn to speak and previous studies have shown that even among children with similar spoken skills, those who gesture more frequently during early life tend to know more words later on. Rowe and Goldin-Meadow have shown that differences in gesturing can partly explain the social gradient in vocabulary size.
They studied the actions of 14-month-old babies from 50 local families of various backgrounds. They videotaped each baby engaging in ordinary activities with their parents for 90 minutes and noted every time they spoke or used gestures to communicate. Only actions with meanings counted - waving goodbye was a gesture, but opening a book was not. Rowe and Goldin-Meadow were particularly interested in how many different meanings they managed to convey through actions - for example, pointing at a dog meant "dog".
At this early age, a child's social background had no impact on how many words they could speak, but it did affect their use of gestures. Toddlers from richer families conveyed more meanings through gestures than those from poorer ones. Children typically start gesturing at about 10 months of age, so according to these results, it takes less than 4 months for a social gradient to develop. At that point, many babies haven't started speaking and among those that have, there is no rich-poor gap in their use of words. But in more silent channels of communication, that gap is already evident.
It probably develops because richer parents gesture more extensively towards their children and indeed, children expressed more meanings through gestures if their parents did so to them. When Rowe and Goldin-Meadow adjusted for parental gesturing, the link between wealth and a child's use of gestures was severely weakened.
These early differences had consequences later. A child's "gesture vocabulary" at 14 months of age predicted the number of words they knew between the ages of four and five. And this link explained some but not all of the connection between wealth and vocabulary size.
Through gestures, children could give children a chance to familiarise themselves with certain meanings at a point when they don't know how to represent them verbally. Alternatively, it's possible that gestures build vocabulary indirectly, by prompting reactions from parents. A baby who points at a dog might get a "Yes, that's a dog" from their mum. Indeed, Goldin-Meadow previously found that when mothers "translated" their child's gestures into words, the child would incorporate those words into their vocabulary several months later. In a way, children "use their hands to tell their mothers what to say".
Obviously, gestures aren't the only thing explaining the link between social status and child vocabulary but Rowe and Goldin-Meyer's work shows that they are important. It suggests that parents may be able to use their hands to improve their child's later communication skills by, even before they can actually speak.
Reference: M. L. Rowe, S. Goldin-Meadow (2009). Differences in Early Gesture Explain SES Disparities in Child Vocabulary Size at School Entry Science, 323 (5916), 951-953 DOI: 10.1126/science.1167025
More on gestures:
Gestures reveal universal word order, regardless of language
Chimps show that actions spoke louder than words in language evolution