By Anne Harding
NEW YORK (Reuters Health) - Infants with profound hearing loss may process visual stimuli more slowly than hearing infants, new findings suggest.
"Our study shows that deafness or lack of auditory input from birth already starts to have a profound impact on cognitive development really from the first months of life," Dr. Claire Monroy of Ohio State University Wexner Medical Center, in Columbus, told Reuters Health by phone. "It's a really critical thing to remember when considering different intervention options with families."
The auditory system is critical to cognitive development, Dr. Monroy and her team note in PLOS ONE, online February 6, and there is some evidence for cognitive differences between children with and without hearing loss.
This flies in the face of conventional wisdom, which would suggest that other senses may help deaf individuals compensate, for example by developing extra-sharp visual skills, the researcher pointed out.
"There are a lot of misconceptions about that, both within the research community, within the medical community, and within the general public," she said. "This is something that our study starts to clarify a bit."
Dr. Monroy and her colleagues compared visual habitation in 23 infants with severe to profound hearing loss and 23 age-matched, typically developing controls. The infants were awaiting cochlear implantation, which the U.S. Food and Drug Administration has only approved for children 12 months and older. Infants ranged in age from about seven to 22 months.
The authors measured how long it took for the infants to habituate to a visual stimulus and the infants' look-away rate during dishabituation, which are complementary measures of cognitive function and attention.
It took significantly more trials for the deaf infants to reach habituation, and they also had a significantly lower rate of looking away from the stimulus. Looking time was correlated with look-away rate.
For the first four trials, growth-curve analysis showed that looking time slopes were significantly different for the deaf and hearing infants. The number of trials it took a deaf infant to habituate was correlated to their raw PLS-4 Total Language scores, while infants who habituated more quickly had higher language scores.
"Our data point to slower processing rather than for example richer or deeper processing," Dr. Monroy said.
She noted that cognitive function and vision are evaluated in deaf children the same way that they are evaluated in hearing children. "This kind of suggests that might not necessarily be appropriate if their cognitive function is really so different from birth," she said.
"Especially with these children, it's really important to keep the entire child in mind and realize that hearing doesn't develop in a vacuum, the auditory system doesn't operate independently from their other sensory systems," she added.
PLoS One 2019.