OU Researcher Studies How Children with Hearing Loss Learn to Speak

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OKLAHOMA CITY – Cochlear implants give children with profound hearing loss a much better chance to learn spoken language. However, the sounds from a cochlear implant aren’t as clear as natural hearing, making it harder for children to connect the way they move their mouths with the sounds they hear.

Matthew Masapollo, Ph.D., a researcher at the University of Oklahoma College of Allied Health, is studying how children develop the motor skills needed for speech – how the lips, tongue, jaw and other structures work together to animate the vocal tract. With funding from the Presbyterian Health Foundation, he is exploring whether children with unclear sound signals rely more on the feeling of their mouth and tongue to guide their speech movements.

“Speech production is a rich choreography involving the coordination of over 100 muscles – one of the most complex actions a human routinely performs,” said Masapollo, an assistant professor of communication sciences and disorders. “The coordinated muscle movements extend from the larynx up to the lips, engaging the entire vocal tract. It’s amazing to think that these intricate muscle movements performed during a simple exhale can produce sounds that convey the contents of our minds to someone else. That’s why it is incredibly important to develop novel interventions for children who struggle with acquiring speech and language.”

Masapollo’s early experiments show that people with normal hearing depend heavily on what they hear to control speech. When sound is blocked, their speech movements become less precise. But in a paradoxical finding with cochlear implant users, their speech movements improve when the implant is turned off.

“Our hypothesis is that when a person has degraded auditory input, as in the case of cochlear implant recipients, they rely more on the feeling of the mouth to control speech,” he said. “It’s similar to the idea that deaf people are better at lip reading – when auditory input is degraded, they compensate with the intact visual system. It’s the same thing here. Auditory input is degraded, so people rely more on non-auditory information to regulate the movements of speech.”

Masapollo is now testing that hypothesis on a larger scale and with sophisticated equipment called electromagnetic articulography. To use the technology, copper electrodes are attached to a person’s lips, tongue and jaw with non-toxic dental glue. A magnetic field, tracking the position of the sensors, provides a three-dimensional video of how the vocal tract is moving. In addition, an ultrasound probe held under the chin gives an extra look at the tongue while people are talking. In tandem, Masapollo can measure the sound of speech to understand how the movements are shaping the acoustics.

In addition to testing cochlear implant recipients with their implants turned off and on, Masapollo is working with Mark Mims, M.D., and other OU colleagues in otolaryngology (ear, nose and throat specialists) to administer sensory nerve blocks that essentially anesthetize the vocal tract, in order to see how the lack of feeling affects the control of speech movements.

If Masapollo’s hypothesis is correct, it would suggest that the optimal way for deaf children to learn to talk would involve oral motor training, such as a device that helps them feel what it’s like to produce sound, rather than focusing solely on the improvement of their hearing.

“When we produce speech, the lips, tongue, jaw and other structures are working in concert to shape the vocal tract and structure the acoustic signal,” he said. “But many of those movements, particularly those involving the tongue, are hidden within the inner reaches of the vocal tract. So if a person can’t hear the acoustic consequences of those movements, then the body’s sense of movement and touch becomes even more important. Learning to make the most of that sensory feedback may be key.

“There is still so much to know about how a person learns to control the movements of their vocal tract in service to speech,” he added. “That’s why it’s important for us to study ways to help children achieve their full potential if they are born deaf.”