Long before our eyes open at birth, the world around us comes alive through sound. A growing body of evidence now shows that noise—or lack thereof—can also affect the way infants process information through other senses, like vision.
According to new research published today in the journal PLOS ONE, deaf and hearing children show differences in how they process new information beginning early in infancy. The study, which tested infants’ ability to familiarize themselves with new objects, is the first to assess these kinds of skills in children before their preschool years, and may help pinpoint when cognitive differences start to emerge.
“Infants’ earliest experiences are really auditory experiences,” says study author Claire Monroy, an otolaryngology researcher at Ohio State University. “We tend to think we’re such visual creatures, and we certainly are. But we tend to underestimate how important hearing is.”
To measure the early impacts of hearing loss, a team led by Monroy and Derek Houston, also at Ohio State University, studied a group of 46 infants ranging from about eight to 23 months of age, half of whom were deaf. At this age, infants aren’t very verbal, but have a good grasp on a cognitive skill called visual habituation.
When shown an image of a new object, babies will stare at it until they’ve internalized the information and lose interest. The amount of time it takes for a baby to habituate, or start looking away from the picture, Monroy says, is a rough proxy for its ability to process information of all kinds, not just visual. Previous studies have shown that hearing children with shorter habituation times tend to perform better on standardized tests later in life, but on the whole, there still aren’t reliable ways to forecast an individual’s intellectual ability from infancy.
In the study, the deaf babies took longer than the hearing children to look away from the images. Nothing about the task required the infants to listen for noise from their surroundings, but it seems that being hard of hearing at such a young age alters the trajectory of development in more ways than one, Monroy says.
Houston’s research group has a mantra: The ear is connected to the brain. That’s no shocker—but it’s important to know that sound “affects the whole system,” he says. “And now we know it affects the system starting at pretty early ages.”
The researchers are quick to caution that these results shouldn’t be misinterpreted as cognitive impairment, however. Deaf children experience the world differently—but differences aren’t automatically deficits, says Rachel Rangel, a Boston-based audiologist who was not involved in the study. Despite taking a little more time to do so, the deaf infants all successfully familiarized themselves with the new object. It’s possible that their longer habituation times simply reflect an adaptive, alternative way of perceiving the world.
“By virtue of the fact that they get a lot of visual, and not a lot of auditory, information, maybe it’s natural for [deaf children] to spend a greater amount of time scanning their environment,” says Chigusa Kurumada, who studies language learning and processing at the University of Rochester, but was not involved in the study.
It’s also possible that deaf infants are using other strategies to navigate their surroundings that we still don’t fully understand, Monroy says.
Testing that theory will require more research. In the meantime, though, simply knowing that the effects of deafness can crystallize this early may have important implications for therapies for children with hearing loss. Kids who receive cochlear implants, for instance, need to undergo rehabilitation and speech therapy. If sounds are shaping the brain as a whole, Houston says, there may be more at stake when it comes to designing early interventions.
“If these kids need an intervention, the earlier we implement it, the better off they’re going to be,” Rangel says. “Once we kind of unlock what these interactions are forming in a child’s brain, they can give us insight into helping kids develop the best that they can.”