Children with developmental dyslexia confuse letters and syllables when they read. The idea that they may have an underlying problem processing sound was introduced by Paula Tallal, PhD, of Rutgers University in the 1970s, but it has never been tested using brain imaging. Nadine Gaab used functional MRI imaging (fMRI) to examine how the brains of 9- to 12-year old children with developmental dyslexia, and normal readers, responded to sounds, both before and after using educational software called Fast ForWord Language, designed in part by Tallal, a co-author on the study.
Nadine Gaab first tested how the children's brains responded to two types of sounds: fast-changing and slow-changing. These sounds were not language, but resembled vocal patterns found in speech. As Nadine Gaab watched using brain fMRI, the children listened to the sounds through headphones. The fast-changing sounds changed in pitch or other acoustic qualities quickly - over tens of milliseconds - as in normal speech. By contrast, slow-changing sounds changed over only hundreds of milliseconds.
In typical readers, 11 brain areas became more active when the children listened to fast-changing, compared to slow-changing, sounds. Nadine Gaab set this as "normal". In dyslexic children, the fast-changing sounds didn't trigger this ramped-up brain activity. Instead, dyslexic children processed the fast-changing sounds as if they were slow-changing - using the same brain areas, at the same lower intensity. "This is obviously wrong", stated Nadine Gaab.
New research shows that children with dyslexia, compared to typical readers, have trouble processing fast-changing sounds. Scientists believe this prevents them from properly learning syllables when they first hear language, which later causes reading difficulties. In the test above, children listened to two types of sounds: sounds whose acoustic qualities changed quickly, as in normal speech, and slowed-down sounds that changed slowly. Yellow spots indicate brain areas that responded more strongly to fast-changing sounds than slow-changing sounds. Typical readers (Image A) used eleven brain areas more extensively when processing fast-changing as opposed to slow-changing sounds. In contrast, children with dyslexia (Image B) didn't show these differences; they used the same brain areas to the same degree to process both fast- and slow-changing sounds. After computer training, the lesser-used brain regions "awakened" (image C). The dyslexic children's brains processed fast-changing sounds more like typical readers' brains, and their reading improved. Photo: Courtesy of Nadine Gaab, PhD, Children's Hospital Boston.
Infants must correctly process fast-changing sounds, like those within the syllable "ba", in order to learn language and, later, to know what printed letters sound like. Infants use sound processing to grab from speech all the sounds of their native language, then stamp them into their brains, creating a sound map. If they can't analyse fast-changing sounds, their sound map may become confused.
"Children with developmental dyslexia may be living in a world with in-between sounds", stated Nadine Gaab. "It could be that whenever I tell a dyslexic child 'ga', they hear a mix of 'ga', 'ka', 'ba', and 'wa'."
Reading trouble may develop when these children first see printed letters, Nadine Gaab and cognitive scientists believe, because at this stage, the children's brains wire their internal sound map to letters they see on the page. Linking normal letters to confused sounds may lead to syllable-confused reading.
But the brains of the children with dyslexia changed after completing exercises in a computer programme known as Fast ForWord Language developed by Scientific Learning, Oakland, California. The exercises involved no reading - only listening to sounds, starting with simple, changing noises, like chirps that swooped up in pitch. The children then had to respond - clicking to indicate, for instance, whether the chirp's pitch went up or down. The sounds played slowly at first - an easy task for the dyslexic children - but gradually sped up, becoming more challenging. The exercises then repeated with increasingly complex sounds: syllables, words, and finally, sentences.
The repetitive exercises appeared to rewire the dyslexic children's brains: after eight weeks of daily sessions - about 60 hours total - their brains responded more like typical readers' when processing fast-changing sounds, and their reading improved. It's unclear, though, whether the improvement lasts beyond a few weeks, since follow-up tests were not done.
Nadine Gaab has begun recruiting for a new study of preschoolers whose family members have dyslexia. By looking for sound-processing problems on brain fMRI, she hopes to catch dyslexia at an early stage, before the children begin learning to read - and then remediate it through sound training, sparing them from years of frustration and low self-esteem later in life.
She will also investigate what other types of sound training might help dyslexic children. Learning to sing or play an instrument, for example, involves gradual, repetitive, and intense listening and responding to fast-changing sounds.
"We've done a few studies showing that musicians are much better at processing rapidly changing sounds than people without musical training", stated Nadine Gaab. "If musicians are so much better at these abilities, and you need these abilities to read, why not try musical training with dyslexic children and see if that improves their reading?"
Elise Temple, PhD, of Dartmouth College's Department of Education, was the senior author of the study, which was funded by the Haan Foundation and the M.I.T. Class of 1976 Funds for Dyslexia Research. Fast ForWord Language was developed by Tallal; Michael Merzenich, PhD, of the University of California, San Francisco; William Jenkins, PhD, senior vice president at the Scientific Learning Corporation, and Steve Miller, PhD, of Rutgers University.
Children's Hospital Boston is home to the world's largest research enterprise based at a paediatric medical centre, where its discoveries have benefited both children and adults since 1869. More than 500 scientists, including eight members of the National Academy of Sciences, 11 members of the Institute of Medicine and 12 members of the Howard Hughes Medical Institute comprise Children's research community. Founded as a 20-bed hospital for children, Children's Hospital Boston today is a 377-bed comprehensive centre for paediatric and adolescent health care grounded in the values of excellence in patient care and sensitivity to the complex needs and diversity of children and families. Children's also is the primary paediatric teaching affiliate of Harvard Medical School.