By Charlene N. Rivera-Bonet | Waisman Science Writer
For young adults with Down syndrome, understanding speech is not only related to hearing abilities, but it may also be impacted by cognition. A new Waisman Center study shows that factors such as auditory working memory, or the ability to temporarily process, store, and recall information that was heard may play a role in how young adults with Down syndrome process auditory information.
Hearing loss is highly prevalent in individuals with Down syndrome. This may be due to anatomical differences in the ear, and a higher susceptibility to chronic middle ear infections. The study, published in Ear & Hearing, shows that although hearing loss plays a role in the ability of young adults with Down syndrome to understand speech, there may be other compounding factors of similar relevance.
Individuals with Down syndrome can present with cognitive challenges that contribute to difficulties in processing auditory information. “We know that your ability to hear and to communicate is happening in the context of perceptual and cognitive abilities,” says Ruth Litovsky, PhD, Oros Family Chair, professor of communication sciences and disorders and surgery, and senior author of the study. “So, you can’t really ask how somebody hears without also knowing what their cognition is like, because these abilities are highly associated.”
The study investigated two aspects of auditory function in relation to how young adults with Down syndrome understand speech in both quiet and noisy environments. “The first one is called spatial hearing, and assesses how well a source of the sound can be located. And the second one is called speech recognition which assesses how well individuals can understand speech in quiet or noisy situations,” says Kumari Anshu, PhD, postdoctoral fellow and first author of the paper.
Auditory function is involved in everyday communication, for example, when catching up with a friend at a busy coffee shop, which is noisy, we can know where our friend’s voice is coming from, and understand what they say if we can ignore background noise. “Functional hearing is all about everyday communication and navigating our way around the world.” Litovsky says.
They evaluated the ability of young adults with Down syndrome to identify “where” a sound was located in quiet conditions, and “what” the content of sound was in both quiet environments and in the presence of speech interferers.
In the brain and auditory system, the “what” and the “where” pathways mature at different stages of development. Being able to localize a sound is less dependent on cognitive abilities, and is a skill developed very early on. So, even in the presence of hearing loss or cognitive challenges, individuals with Down syndrome may develop compensatory mechanisms by the time they become young adults. This pathway, the study shows, appears to be a relative strength for individuals with Down syndrome, as they were able to accurately tell where the sound was coming from.
The later development of the “what” pathway, however, leaves less room for compensation. Their results revealed that understanding speech, the “what,” in both the quiet condition and in the presence of interferers was a challenge for young adults with Down syndrome with and without hearing loss.
“I think this has practical implications,” Anshu says. “Whether individuals with Down syndrome have hearing loss or not, their speech understanding in noisy situations can be affected. So, in the classroom settings, or in work places, there may be need for extra support, perhaps with visual supports or preferential seating.”
Individuals with Down syndrome present difficulties in auditory working memory, for example, organizing and storing auditory information. This pathway being more dependent on cognitive abilities may contribute to making speech recognition challenging, even in quiet spaces. “We are considering the possibility that the challenge is not only in the hearing domain, but rather an association between hearing and cognition. Because cognition is already affected, especially working memory and language, the combined effects can be compounding,” Anshu says.
Young adults with Down syndrome who had better hearing also had better speech recognition. Similarly, those who had better auditory working memory also showed better speech recognition.
Based on these results, Anshu says, evaluation of functional hearing skills should be incorporated along with hearing loss screenings to develop a more comprehensive auditory profile in this population and create more specific supports.
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