Study investigates roots of language impairment in autism

Understanding the nature of the language impairment in autism and how variations in the pattern of early speech development might correlate with later language function are goals of a project led by CHDD research affiliate Dr. Patricia Kuhl. The project, which is called "Precursors to Language in Autism," is part of the longitudinal study.

In an approach new to autism research, Kuhl, professor of speech and hearing sciences, will use five detailed measures she has refined during 20 years of research in typical language development. The measures test basic abilities that underpin language. She will use them to determine whether language deficits in autism are caused by a fundamental problem in language processing or are a result of social deficits, which may curtail language learning experience. The measures also provide the basis for assessing relationships between patterns of early language development and later language outcomes­crucial information for guiding intervention efforts.

Traditionally, autism research has focused on overall measures of language skills, says Kuhl. "We're going to test very early precursors to language in young children with autism and see whether these precursors predict where the children end up on outcome measures of language development."

A fundamental aspect of language development is the ability to differentiate speech sounds. To determine if children with autism can hear the difference between simple phonetic units, Kuhl will use event-related potential (ERP) techniques like those used by Dawson and Meltzoff (see bottom of story). She will look at a particular measure of electrical activity in the brain known as mismatched negativity (MMN). This measure takes a distinctive shape on the graph of the electrical signal in the brain when it detects a change in stimulation. The first test in the study involves a voice repeating a string of syllables with an occasional syllable that deviates from the one being repeated. For example, the child might hear "ba, ba, ba," then "da," then back to "ba, ba, ba." The presence of MMN reflects whether the child's brain distinguishes between the two syllables.

It's possible that children with autism may not show deficits in discrimination of basic speech sounds. Their language impairment may arise instead from another aspect of fundamental processing­they may be unable to form language categories. This ability typically develops over time as a result of experience, explains Kuhl. Her work has shown that typically developing young babies can discriminate the phonetic building blocks of all the world's languages, but by 6 months they focus on the sounds of their own language. Japanese children respond to different sounds than American children.

Typically developing children listen to the language spoken around them and unconsciously their brains become "wired" to distinguish what they are hearing, says Kuhl. But this process may not occur in autism. Kuhl suggests that deficits in social cognition, which limit an autistic child's interest in people, may interfere with the experience necessary to lay down the wiring. The second test taps the effect of linguistic experience by measuring reaction to prototypical sounds from different language categories.

"These two very targeted measures will help us determine whether the innate structure of language capability in children with autism is different from that of typically developing children," says Kuhl. The third test will examine echolalia, a persistent repetition of sounds exhibited by some children with autism, particularly those whose symptoms are most severe. "We don't know why children with autism produce echolalia," says Kuhl. "But we do know that it is not correlated with good language outcomes."

Imitation is a major part of a typical development, but echolalia is different. By looking at echolalia in a formal measurement situation for the first time, Kuhl hopes to begin to understand what function it serves for children with autism or whether, as it seems, it is the tendency to imitate run amok.

The final two tests in Kuhl's study rely on preference measures. One will assess whether a child with autism is able to correlate the sight of a person's face while speaking with the sound of a voice. The other will document what kinds of sounds a child with autism would rather listen to. Some evidence suggests that children with autism prefer sounds made by objects rather than language sounds.

Each of the five measures taps a different kind of language ability, ranging from basic perception of sounds to higher levels of cognitive processing. Combined, the measures make a language profile of each child that will answer fundamental questions about language impairment in autism. And, in conjunction with other measures from the longitudinal study, these profiles will deepen understanding of autism in general.

Researchers in the longitudinal study will map electrical activity in the brain using ERP techniques. Data is gathered by a net of sponge-tip electrodes that a child wears while he or she performs language and neuropsychological tasks.

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