Born months prematurely, infants in neonatal intensive care units (NICU) could be starting their lives surrounded by the wrong sounds, according to research presented Saturday at the 2016 AAAS Annual Meeting.
New studies of what these infants hear and don't hear during their weeks in the hospital suggests that some may be missing out on the positive impact of a mother's voice and heartbeat, and are instead training their brains to prioritize background noise over human voices, said Amir Lahav, an assistant professor of pediatrics at Harvard Medical School.
In Lahav's studies, NICU infants who heard recordings of their mothers' singing, reading stories, and talking softly, along with their heartbeats, gained more weight and increased the size of their brain's auditory cortex compared to infants who listened mostly to the white noise of the fan inside their incubators.
These infants exposed to maternal sounds are also better at picking out female voices in a noisy environment once they are ready to leave the hospital, according to his preliminary research.
"The hospital environment that we currently have for those very premature babies doesn't match the developmental needs of the baby," Lahav said, noting that some premature infants grow up to have language and attention deficits that affect their later learning.
"That gap between the acoustic environment in utero, as opposed to the acoustic environment in the NICU," he said, "may account for some of these developmental disabilities we see down the road."
For instance, he said, a premature infant who spent critical developmental weeks listening to white noise in the hospital may "prioritize" that kind of noise later in life, preferentially tuning into background sounds instead of paying attention to the voice of a parent or teacher.
Nan Bernstein Ratner, Rochelle Newman, Lori Leibold, and Amir Lahav at the 2016 AAAS Annual Meeting. | Ashley Gilleland/ AAAS
"We tend to think of kids as being the source of noise more than the victims of noise," said Nan Bernstein Ratner, a professor of hearing and speech sciences at the University of Maryland. A wealth of new studies, she said, suggest that children learn language from listening to others but are not as well-equipped as adults to cope with the cacophony of modern life.
"What a child hears in a noisy environment is not what an adult hears," agreed Lori Leibold, director of the Center for Hearing Research at Boys Town National Research Hospital. In her studies of school-age children, including those with hearing problems, she and her colleagues have found that children have trouble identifying speech and learning language in the midst of noise, especially speech from competing voices.
"The language learning systems of the brain presumably evolved in far-quieter ambient environments than present-day settings," said Rochelle Newman, chair of the University of Maryland's department of hearing and speech sciences.
Newman's studies show that toddlers in particular can recognize speech in noise only at relatively soft noise levels, "and often they fail to do so at noise levels approximating those found in typical daycare centers," she said.
"We need to be much more aware of the impact that this noise might have on children," Newman said, "and make a point of trying to turn off background television, background radio, background noise sources for at least some of the time when we're interacting with our children, to give them the best opportunity to learn from that input."