The same hearing test has the potential to improve the ability to identify these children, many of whom become discouraged with school because of frequent failures tied to their language difficulties.
The language disorder, known as specific language impairment (SLI), is affects approximately three to six percent of children who are normal with the exception of varying degrees of difficulty understanding and expressing spoken language. Many but not all children who have reading problems fall into this category.
"SLI has sometimes been viewed as being specific to language," said Beverly Wright, Ph.D. who is currently at Northwestern University in Evanston, Illinois and was the primary investigator of the study. Dr. Wright used a different approach. "I decided to use my background in psychoacoustics to test the ability of these children to process non-speech sounds or sounds unrelated to language," she explained. "Our team was astounded by what we observed."
What they had observed were clear and distinct differences between the ability of all of the children in their study with SLI to process brief tones in special sound contexts as compared to normal children. The differences depended on where the tones were placed in time in relation to other sounds as well as on the frequencies (pitches) of the tones in relation to the frequencies of other sounds.
Children enrolled in the study listened for brief tones that were presented either before, during or after special kinds of noise. The intensity of the tones was increased until the children could detect them. Long tones were used at first to train the children to the task.
"The children with SLI performed equally with their normal peers when the tone was long," explained Dr. Wright. "Differences were observed, however, when the tone was short, indicating that the length of the tone was a factor in their ability to process the sounds."
The children with SLI performed more poorly in all test conditions compared to the normal children, when the tone was short. In addition, the task was easiest for the normal children when the tone was presented just before the noise whereas the children with SLI experienced the most difficulty under this condition.
Varying the frequency of the surrounding noise also affected performance. Both groups of children performed better when a "notched" noise, or a noise that excluded frequencies close to the tone, was used. If the notch became wide enough, the performance of the SLI children approached that of the normal children, indicating that these children had difficulty separating sounds similar in frequency.
What does this have to do with language? Words are made up of phonemes or speech sounds, which are strung together. For example, "baby" is made up of four sounds- "buh," "ay," "buh," "ee" -which are strung together very quickly. Sentences are made up of many words and therefore contain longer series of sounds. Put several sentences together, as in conversation, and you have an even longer series of rapidly strung together sounds. And these sounds occur in different contexts. The "b" sound in "your baby" is different from the "b" sound in "his baby," simply because the "b" is preceded by a different speech sound in each instance. A child who has problems perceiving rapid sounds or sounds in certain contexts will have problems learning, understanding and expressing spoken language.
Dr. Wright and her colleagues are continuing research to train children to overcome their auditory processing difficulties and thus improve their language ability and subsequent school performance.
"This research offers a fresh approach to a perplexing problem that often leads to continual failure in school," commented James B. Snow, Jr., M.D., Director of the National Institute on Deafness and Other Communication Disorders (NIDCD), National Institutes of Health, which provided partial support for this research. "The NIDCD is proud to support Dr. Wright’s research which will improve the lives of children with SLI."
Scientists at the University of California San Francisco and the University of Florida, Gainesville conducted this research with partial support from the National Institute on Deafness and Other Communication Disorders (NIDCD), National Institutes of Health. The NIDCD conducts and supports biomedical and behavioral research and research training on normal mechanisms as well as diseases and disorders of hearing, balance, smell, taste, voice, speech and language affecting 46 million Americans.