Cochlear implants (CIs) are a technological advancement in hearing support on par with the advent of the hearing aid more than a century ago. Approximately 118,000 adults and 65,000 children in the United States are now using them to participate more fully in the hearing world.
Enormous variability has been noted in the benefits of CI use and its reported effects on individual performance, the perception of performance by patients and clinicians, and the impact on quality of life, says Aaron Moberly, M.D., an otolaryngologist at the Bill Wilkerson Center at Vanderbilt University Medical Center.
“About a third of patients could be considered not to perform well with their implants,” Moberly said. “Traditional means of predicting who those individuals will be are very limited, based on the assessments we have used.”
Outcome variability typically has been based on demographic, audiologic, and surgical factors, Moberly explained. Now, researchers at Vanderbilt are investigating the impact of underlying cognitive and linguistic mechanisms, as well as implant-users’ auditory and social experiences, to broaden assessment measures. The goal is to more effectively predict, explain and improve patient outcomes.
The team is also trying to gain a better understanding of how patients perform in their everyday lives. Conventional assessments for CI users involve idealized speech materials developed in well-controlled laboratory environments. The same users scoring high on these tests may display significant communication difficulties in their daily activities.
“If we better understand what outcomes patients really care about, we can better counsel them and hopefully intervene early on to optimize their experience,” Moberly said.
Relevance of Linguistics
In 2022, Moberly and Terrin Tamati, Ph.D., co-director of the Cochlear Implant Cognition and Communication Lab at Vanderbilt, and David Pisoni, Ph.D., Distinguished Professor of Psychological and Brain Sciences at Indiana University, wrote a chapter for the Annual Review of Linguistics on outcomes in adult and pediatric cochlear-implant users. Specifically, they focused on the role of linguistics research in helping address CI variability, improve clinical assessment tools, and develop new interventions to better reflect real-world environments.
“Previous research has suggested that hearing loss negatively impacts how we process phonology, meaning the sounds of our language,” Tamati said. “By using non-auditory tasks to assess phonological processing in adult CI users, we are describing the important role that individual abilities in phonological processing play in predicting and explaining speech-recognition outcomes.”
Moberly agreed, adding that the “findings suggest that what helps experienced CI users understand speech in adverse listening conditions – specifically, the ability to quickly access words stored in memory – may be somewhat different from the abilities used before surgery to predict a patient’s adaptation to the CI.”
Cognitive Measures Matter
Moberly and Tamati are now interested in how visual measures add to the equation, examining factors in CI success that extend beyond sensory perception, to issues involving brain and language functions.
In their review chapter, they reference studies showing how lip-reading and other visually based linguistic processing aids can help people with sensorineural hearing loss maintain stronger and more robust phonological representations.
Even in listeners with typical hearing, studies have shown varying levels of speech recognition, suggesting that several core neurocognitive skills underlie individual differences in speech recognition abilities.
Outcomes reflect the downstream contributions of an information-processing system that works to understand spoken language, as delivered via electronically-generated signals, to the hearing nerve.
Toward Comprehensive Assessments
Moberly, Tamati, and René Gifford, Ph.D., Fred H. Bess Chair in Audiology and director of the Cochlear Implant Research Laboratory at Vanderbilt, are working to improve CI outcomes by combining their specialties. They are putting cognition, linguistics and sensory factors – all three – at the forefront.
“Next, we plan to develop and test a battery of measures of visual cognitive and linguistic testing,” Moberly said. They plan to examine auditory abilities, the auditory-social experience, and novel outcome measures assessed in quiet surroundings as well as noisy environments.
This diversity will help predict whether someone will succeed using CI.
“To my knowledge, this effort to look across a broad spectrum of factors contributing to outcomes is unique to our team,” Moberly said. “This approach is largely thanks to the fact that we are powered by a high-volume CI center.”
