Language disorder reveals complexity of understanding mental processes

How is language acquired? We don't have to teach our children to speak; instead they just seem to pick it up on their own. Because language is acquired so readily, the study of language acquisition can be a messy business. What portion of language ability is "hard wired" into the brain, and what portion of it is "learned"? Or is the ability to learn what's hard-wired?

One way researchers have found to study how healthy children learn language is to study those with disorders. If we can learn how a brain malfunction affects language learning, then the specific characteristics of the malfunction can give insight into how a normal brain works.

For example, SLI, or specific language impairment, is a condition that affects millions of children. While many children suffering from the condition eventually attain language proficiency, they can have difficulty in school because their ability lags behind other students. Speaking ability appears to be unimpaired, and cognitive abilities other than language are not affected. While vocabulary learning seems to be mainly delayed, there is some evidence that SLI sufferers never attain normal ability with grammar.

However, many studies focusing on language ability and language learning in children with SLI only assess language learning in artificial situations: ability to repeat new words or memorize lists of words. Janice Horohov and Janna Oetting of LSU wanted to know if they would find additional differences between kids with SLI and normal kids when they learned new words in a more natural situation ("Effects of Input Manipulations on the Word Learning Abilities of Children With and Without Specific Language Impairment," Applied Psycholinguistics 2004). So Horohov and Oetting taught kids new words the same way much new vocabulary is learned: by reading them stories—Wake Up, Sun by David Harrison, and Snug Bug by Cathy East Dubowski and Mark Dubowski.

To ensure that the kids didn't already know the new words, Horohov and Oetting replaced 16 of the words in the stories with nonsense words. They also varied the rate at which the stories were read (slow or fast) and they rewrote each of the stories with simple and complex sentences (Simple: "The chicken was very excited. She kootled her wings in the air." Complex: "Chicken, because she was so excited, kootled her wings in the air.").

There were three groups of children: 18 with SLI, averaging age 6; 18 without SLI who were the same age, and 18 younger kids (about four and a half years old) whose language ability matched the SLI kids. This language matching presents a bit of a problem for researchers. They want to understand how children with SLI develop differently, but what is the appropriate comparison group? The children with matching language ability have fewer cognitive and social skills. They might not even be potty-trained. But their agemates are possibly at a different stage in language development. Studying all three groups is the best possible compromise, but still can't offer a true comparison.

Horohov and Oetting found that when the stories were read quickly, the SLI children learned new words at about the same proficiency as the language-matched group (after reading the book, children were given a multiple-choice "test" where they helped the experimenter understand what the "silly words" meant by pointing to a picture corresponding to the meaning), but not as well as the normal children their age.

However, when the stories were read slowly, the kids with SLI were able to learn the words more accurately than the language-matched group, and almost as well as the normal kids their own age. Reading quickly or slowly did not affect either group of normal kids; and the complex sentences posed no additional difficulty for any group, including the SLI group.

So one symptom of SLI appears to be a slowing of processing for certain aspects of language. The ability is present, but it cannot be executed as rapidly as in normal children. Horohove and Oetting suggest that reading and speaking slowly could be a good way to help children with SLI learn vocabulary more rapidly.

But perhaps equally importantly, this experiment adds one more piece to the puzzle of understanding how we learn language. Having the ability to learn language is useless unless that ability can be processed in real time; rapid processing of language is something we take for granted—until that ability is lost.