The way children learn may determine the building blocks of language, suggests a study of deaf Nicaraguan children.
Ann Senghas of New York's Columbia University, US, and colleagues studied three generations of deaf schoolchildren from the Nicaraguan capital, Managua.
The first deaf schools were established in 1977, giving many deaf children their first a chance to interact with one another. Pupils from these schools gradually developed their own form of hand-based communication, known today as Nicaraguan Sign Language.
Senghas and colleagues showed deaf pupils a video of a cartoon cat tumbling down a hill and asked them to describe the event using sign language.
They found that older students used hand signals resembling the gestures employed by hearing people, mimicking the entire event physically. But younger pupils - who had interacted with other deaf children from an early age - used a more complex series of signs. They split the scene into component parts and arranged these sequentially to convey the incident.
The constructions resemble the way words and sentences are built in verbal languages, using segments structured in a linear fashion. This indicates that way the younger children learnt the sign language helped reshape it according to these linguistic rules.
"Our findings indicate that children have a learning mechanism with a bias towards linear and hierarchical organisation of information," says Sotaro Kita at the University of Bristol, UK, and one of the team. "It may tell us why languages all have this linear, hierarchical organisation of information."
Languages the world over exhibit similar structural features, perhaps indicating that humans have a biological predisposition to communicate in this way. The new study suggests that the way children learn a language may play a critical role in constructing these linguistic rules.
The new study may also provide unique insight into the way language evolved, says Karen Emmorey, an independent linguistics expert from the Salk Institute in California, US. "It tells us about the way language emerges," she told New Scientist. "The exciting thing is that there's just no way to get at this data for spoken languages as you can't go back in time."
Pre-adolescent children typically possess better linguistic learning abilities than adults, making it easier for them to learn a new language. But this ability normally disappears around adolescence and why this should happen remains unclear.
Kita suggests that this could have had an evolutionary advantage, helping to reinforce linguistic bonds by making it more difficult for those who grew up outside of a social group to learn its language.
Journal reference: Science (vol 305, p 1779)
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