A study published in Scientific Reports challenges longtime notions about how deaf children learn to read.
Vanderbilt Health researchers report that many prelingually deaf children who use cochlear implants (CIs) achieve age-typical language and reading comprehension, even though their ability to process speech sounds is reduced.
The findings present a paradox: In hearing children, comparable deficits in phonological processing, or the ability to discriminate and manipulate speech sounds, are associated with severe reading disorders. In this study, deaf children with CIs often read successfully, suggesting they may rely on alternative cognitive and neural pathways for literacy.
“Previous studies of reading in deaf children over the last century have universally highlighted difficulties in learning to read,” said Stephen Camarata, PhD, CCC-SLP, professor of Hearing and Speech Sciences. “An underlying assumption has been that an inability to process speech sounds causes these poor reading outcomes. This study reveals that poor auditory processing need not result in poor reading outcomes in deaf children.”
According to Camarata, adult cochlear implant users benefit from preexisting neural organization of the auditory cortex so that the signal from the CIs essentially deceives the brain into filling in missing information. Because prelingually deaf children receiving CIs do not get this benefit, it is an “intriguing scientific conundrum as to how they are able to essentially attain typical levels of language ability and reading comprehension,” he said.
Hearing children with this same profile of poor speech sound processing would be likely to have severe reading disorders. This suggests that deaf children using CIs are developing alternative pathways and processing strategies to learn to read.
Researchers administered a comprehensive battery of standardized tests to 47 prelingually deaf children with CIs, with an average age of 8. Study co-authors Mackenzie Lighterink, AuD, CCC-A, a doctoral candidate in Hearing and Speech Sciences; René Gifford, PhD, chief of Audiology and Research at Hearts for Hearing; and Rob Labadie, PhD, MD, adjunct professor of Otolaryngology-Head and Neck Surgery, have developed methods for optimizing CI implantation and signal processing, but spectral resolution, needed to resolve key elements of the speech signal, remains relatively distorted.
As expected, phonological processing scores fell well below age-normative levels, often into the clinically significant deficit range. What surprised researchers is that receptive and expressive language skills and reading comprehension were frequently within the typical range.
“Because academic outcomes and broader access to information is directly predicated on literacy and reading ability, it is very exciting to see progress in this long-standing challenge,” Camarata said. “Because I have been working to support language and reading outcomes for more than 40 years, and supporting communication and educational development of children with disabilities, seeing the majority of these deaf children read and comprehend what they read at or above grade level reading is truly miraculous.
“Prior to the development of cochlear implant technology, very few deaf people could read beyond second or third grade levels, and many could not read at all. In the study, it was especially striking that some of the children in middle school were reading at high school level. And this success leads to new discovery avenues: How are they able to do this without doing well on speech processing tasks usually required to develop reading comprehension?”
For more than 30 years, dominant models of reading development have emphasized phonological processing as a foundational requirement for reading comprehension. The results of this study suggest that this relationship may not be universal.
While phonological processing, language ability and reading comprehension were correlated, analyses showed that verbal language skills — not phonological processing — were the strongest predictor of reading comprehension in children with CIs. Even severe weaknesses in processing nonwords, a classic marker of phonological decoding ability, did not preclude strong reading outcomes.
“In the 1980s, models of reading development highlighted the key role of speech processing, along with verbal language development as foundational to reading and reading comprehension,” Camarata said. “And there are many compelling neuroimaging studies, including those conducted by James Booth and other studies by Laurie Cutting here at Vanderbilt demonstrating the crucial role of speech processing in reading. The sheer number of replicated findings in these types of studies for reading in children without hearing loss suggests that the outcomes in our study would be highly unlikely.
“Although the cochlear implants do significantly improve hearing in deaf children, speech processing remains relatively poor. So, the question arises as to which compensatory pathways and neural mechanisms are being built and activated to enable reading comprehension when speech processing remains relatively poor.”
The study may have practical consequences for how educators and clinicians support deaf children with cochlear implants. Phonological awareness and decoding instruction are widely emphasized in literacy interventions for children with hearing loss. While such instruction remains important, the findings suggest that strengthening broader language skills — such as vocabulary, morphology and sentence comprehension — may play a particularly critical role in supporting reading comprehension.
“This study calls into question long-standing assumptions about how reading develops and underscores the importance of studying outcomes that matter most to children with cochlear implants and their families,” said Melissa Duff, PhD, the Vickie and Thomas Flood Professor of Hearing and Speech Sciences and chair of the department. “It reflects our department’s commitment to research that not only advances theory but also can have meaningful implications for the next generation of research, intervention and educational policy.”
The authors emphasize that more research is needed, including longitudinal studies and neuroimaging work, to uncover the precise mechanisms that allow deaf children to read successfully despite limited access to speech sounds.
The research was supported by the National Institutes of Health (grants R01DC017683, UL1TR000445).
