NORTHWESTERN (US)—In noisy environments, the brain sometimes struggles to identify specific sounds and encode them properly. New findings suggest this neural hiccup can make a big difference in how words are read, especially for those with poor reading skills.
“What your ear hears and what your brain interprets are not the same thing,” explains Nina Kraus, Hugh Knowles Professor of Communication Sciences and Neurobiology and director of Northwestern University’s Auditory Neuroscience Laboratory, where the study was conducted.
“The ‘b,’ ‘d,’ and ‘g’ consonants have rapidly changing acoustic information that the nervous system has to resolve to eventually match up sounds with letters on the page,” she adds.
The Northwestern study is the first to demonstrate an unambiguous relationship between reading ability and neural encoding of speech sounds that previous work has shown present phonological challenges for poor readers.
The research, which was published July 13 in the Proceedings of the National Academy of Sciences, offers an unparalleled look at how noise affects the nervous system’s transcription of “ba,” “da,” and “ga”—three little sounds that mean so much to literacy.
By offering a neural metric sensitive enough to pick up how the nervous system represents differences in acoustic sound in individuals, the researchers were able to reflect the negative influence of background noise on sound encoding in the brain.
“There are numerous reasons for reading problems or for difficulty hearing speech in noisy situations, and we now have a metric that is practically applicable for measuring sound transcription deficits in individual children,” explains Kraus, the study’s senior author.
“Auditory training and reducing background noise in classrooms, our research suggests, may provide significant benefit to poor readers.”
For the study, electrodes were attached to the scalps of children with good and poor speech-in-noise perception skills. Sounds were delivered through earphones to measure the nervous system’s ability to distinguish between “ba,” “da,” and “ga.”
In another part of the study, sentences were presented in increasingly noisy environments, and children were asked to repeat what they heard.
“In essence, the kids were called upon to do what they would do in a classroom, which is to try to understand what the kid next to them is saying while there is a cacophony of sounds, a rustling of papers, a scraping of chairs,” Kraus explains.
In a typical neural system there is a clear distinction in how “ba,” “da,” and “ga” are represented. The information is more accurately transcribed in good readers and children who are good at extracting speech presented in background noise.
“So if a poor reader is having difficulty making sound-to-meaning associations with the ‘ba,’ ‘da,’ and ‘ga’ speech sounds, it will show up in the objective measure we used in our study,” Kraus explains.
Reflecting the interaction of cognitive and sensory processes, the brainstem response is not voluntary.
“The brainstem response is just what the brain does based on our auditory experience throughout our lives, but especially during development,” Kraus says. “The way the brain responds to sound will reflect what language you speak, whether you’ve had musical experience, and how you have used sounds.”
In related research, Kraus has also shown that the ability to hear speech in noise is enhanced in musicians.
“The very transcription processes that are deficient in poor readers are enhanced in people with musical experience,” Kraus says. “It makes sense for training programs for poor readers to involve music as well as speech sounds.”
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