A landmark University of Colorado at Boulder study has confirmed that early detection and intervention involving infants with hearing loss has startlingly positive effects on their subsequent language abilities.
Of 368 deaf or hard-of-hearing infants, those identified within the first six months showed significantly more expressive vocabulary development by three years of age than those identified after six months, said Christine Yoshinaga-Itano, chair of CU-Boulder聮s speech, language and hearing sciences department. The results are similar to, but more illuminating, than a 1998 CU study. That study showed language development in 72 babies identified with hearing disorders before they were six months old was significantly better than 78 infants who were not identified with such problems until after six months.
"What we have learned is that it is critically important to identify hearing loss and provide intervention as early as possible in a child聮s life," said Yoshinaga-Itano. "Our current intervention techniques are not as successful when children are identified with hearing loss after they reach the age of six months."
The intervention method in the study was parent instruction that included the use of hearing aids, sign language education and auditory and speech development assistance.
The new study conducted by Professor Yoshinaga-Itano and Assistant Professor Allison Sedey will be published in The Volta Review, a prestigious U.S. journal for the education of deaf children or children with hearing loss. The results of the study were presented at the American Association for the Advancement of Science annual meeting in Washington, D.C., Feb. 17 to Feb. 22.
"The urgency for early intervention is very high, " said Yoshinaga-Itano. "Fortunately, the screening of infants for hearing loss has been spreading like wildfire in this country and overseas in the past several years."
In 1994, Yoshinaga-Itano and her colleagues began studying language and speech development in deaf and hard-of-hearing children with a $2.3 million grant from the National Institutes of Health. In 1996, CU was awarded $1.3 million from the Maternal and Child Health branch of NIH to coordinate the implementation of universal newborn-hearing screening programs in Colorado and 18 other states. Today, 27 states have legislation to establish newborn-hearing screening programs.
"Once the medical community saw our 1998 study, physicians began to actively support universal infant-hearing screening and things began moving very fast," Yoshinaga-Itano said. "The new studies should help the U.S. Health and Human Services Department meet its goal of universal newborn hearing screening in all 50 states as part of its 聭Healthy People 2010聮 initiative."
The new CU-Boulder study also showed that children with hearing loss could develop intelligible speech even when they had very little speech ability in the first few years of life. In addition, the researchers found that babble in the first year of life is not a reliable predictor of subsequent speech intelligibility. Instead, the significant predictors for speech intelligibility were language development and individual degree of hearing loss, she said.
Surprisingly, the researchers also found that children who had only mild hearing loss, who were identified early and provided with intervention nevertheless had speech that was much more similar to deaf children than to children with normal hearing in the first year of life, Yoshinaga-Itano said.
But infants with hearing loss who received early intervention managed to maintain language development that was within the normal range through their early childhood, she said. The researchers are hopeful that the children will be able to maintain the same level of language development as they grow older.
"Fortunately, we now have an opportunity to follow a large, new population of children with hearing loss throughout their school experience and discover new things about language development that would not have been possible before," she said.
The average $25 hearing screening test per child is a small price to pay compared to the costs to parents, guardians, school systems and society for those children who go undiagnosed and untreated and who often leave school with language levels too low to fare well in society, she said. Because of this, many cannot find employment and end up receiving disability support.
"But early detection and intervention of hearing loss gives these children the opportunity to achieve like hearing children and allows them to become equal members of our society," Yoshinaga-Itano said.
Out of the roughly 4 million children born annually in the United States, it is estimated between 12,000 and 24,000 suffer some sort of hearing disorder. Of these, less than 10 percent are born profoundly deaf, she said.
"When we began this project, we had no idea how critically important the first six months of life were to the development of language abilities in children with hearing loss," she said. "It was a surprise that has revolutionized what professionals do in their identification and intervention processes."