Language researchers often study people with certain kinds of brain disorder to understand the nature of human language. For example, they study people with autism, because they have difficulty with both language and social interactions. Scientists have also looked at people with a much rarer disorder, Williams Syndrome, which also causes problems with language.
People with Williams Syndrome are elf-like in appearance. They have small bodies, wide mouths and upturned noses. Individuals with this syndrome have a number of unusual mental characteristics. On the one hand, they are socially outgoing and very sensitive to people's moods. On the other hand, they have trouble understanding complex thoughts and emotions, or identifying another person's intentions or beliefs. As a result they are talkative, yet what they say is often slightly out of context. They also have an average IQ of about 60.
Language researchers were originally drawn to study people with Williams Syndrome because their language skills seemed surprisingly good, given their low intelligence. The disorder appeared to be the opposite of autism, in which people can have normal IQ, but few language skills. Some scientists thought that the syndrome showed that language existed as a separate unit that functioned in the brain even when many other mental functions were limited.
Over time though, it has become clear that people with Williams Syndrome do have problems with language. As babies, they start to talk much later than normal infants. And when they do start to talk, they use words randomly. As they grow older, their language improves to the extent that they learn to use the right words and use them with good grammar.
There appear to be several reasons for this improvement. They have a good memory for words, which gives them an impressive vocabulary for their mental age. Another reason is their "overfriendliness" and "social drive," says Ursula Bellugi, a cognitive neuroscientist at the Salk Institute in California.
This is unlike people with autism, who tend to be socially isolated. Their motivation to talk to other people is so strong that it helps them overcome some of their initial problems with language. Bellugi says that one thing Williams Syndrome shows is the close link between language and social interactions. "We are learning how language is essentially used for social purposes," she says.
But their social skills and memory are not enough to take their language to the level of a normal person their age. To use language fully, people need sophisticated social skills that people with Williams Syndrome don't have. One of these is something called theory of mind. It's the ability to understand the thoughts and feelings of the person we are talking to. Helen Tager-Flusberg, a neurobiologist and psychologist at Boston University, says that people with Williams Syndrome can't do this very well. They don't have a "sound theory of mind," she says. The inability to understand the world from another person's point of view means they often end up missing the point in a conversation.
Annette Karmiloff-Smith, of the Institute of Child Health in London, has studied Williams Syndrome for nearly two decades. She says the disorder shows that "many different things contribute to the normal onset and development of language."