Early Detection of Hearing Disabilities
Every time my kids get a check-up, it strikes me that pediatricians are checking eyes and ears in the same way they’ve been checking for at least the last 50 years (yep, I just turned 50). True, a general practitioner will typically only screen for evidence of deeper issues and then refer onward if something suspicious or ‘outside the normal range’ is found. But in light of my 11 year old son being diagnosed with APD (Auditory Processing Disorder), it occurs to me that the current hearing testing conducted by schools and pediatricians is woefully inadequate because it is incapable of discovering the range of hearing disabilities we know to be present in the population today. Instead, we end up waiting until these hearing disabilities manifest in children as inability to read, write, and learn at grade level, and often failing or borderline performance by older students who are unable to learn in a typical classroom environment and are likely suffering emotional and psychological harm.
To appreciate this difference let’s consider current vision testing. Children are asked to discern whether arrows are pointing up down or sideways, or whether a shape is a smooth circle or star with points, and whether one shape is bigger or smaller than another, and so on. But what if the vision test merely involved flashing a dot in different areas of a screen and asking whether the person sees anything? And they only need to answer Yes or No to determine vision health? In that case, pretty much everyone except the most extreme visually disabled individuals would ‘pass’. Fortunately that doesn’t happen and so we don’t have to wait until kids suffer numerous physical injuries from walking into tables and falling down steps, or flunk out of pre-school before we begin to suspect that there are vision problems.
So why are we still simply asking kids to discern mere audiometric thresholds when we know that other attributes of sound such as rhythm, pitch, timbre, and localization are just as important to function well in our current environment? The unfortunate truth is that the professional community cannot come to an agreed-upon set of cues that reflect appropriate hearing ability and fidelity. Part of the frustration is that neurobiologists and neuropsychologists don’t really fully understand the mechanisms of how people hear and what the brain does with what the ear detects. But the research is ongoing and our understanding continues to develop and deepen. Findings in the last couple of years that I’ll share are truly exciting because they bring us closer to a time when some simple, early diagnostics will reveal a more detailed picture of a person’s hearing ability and alert parents and professionals of issues to be addressed early on in the child’s life.
A few years ago, studies by Ruggles, et.al. demonstrated quite elegantly the critical role of temporal cues on sound perception and analysis or decoding. What’s most exciting about the work is that they also designed and demonstrated a series of tests which detected temporal dysfunction. Temporal cues are things like vowel sounds (long or short), articulation of consonants, stress or inflection in a word or phrase. Researchers and clinicians have known for decades that temporal cues are important. But reliable, definitive screening and diagnostic methods have been lacking. The tests described in the Ruggles report were objective, uncomplicated, easy to grasp, and relatively easy to administer and interpret. In short, the team showed the feasibility and benefits of conducting more sophisticated auditory screening tests.
As parents and therapists, we’re always promoting awareness of the spectrum of hearing and learning deficits. But this is the sort of work that helps arm us better to promote the need for developing and implementing proactive screenings that are reliable and feasible. Now, ‘fast-forward’ a few years to September 2014 when another article caught my eye and it is exactly the kind of big news we need! I say this because the research and its implications are so elegant that it’s easy for just about anyone to grasp the work and its implications.
Early Detection of Hearing Disabilities
Nina Kraus and her colleagues of the Auditory Neuroscience Laboratory at Northwestern University study the changes in the brain that happen with auditory learning. The findings in some of their most recent work with very young children hint at another type of diagnostic for disabilities in speech processing. The exciting thing here is that it’s for children that have not even begun to read or exhibit other higher level language skills yet!
Much of the laboratory’s work has centered on the idea that beat synchronization ability (i.e. matching a given rhythm or beat) is closely related to the ability to process temporal cues – just like the ability in encoding speech. In this way, poor neural precision may contribute to both rhythmic and phonological deficits. Indeed, previous work has shown that beat synchronization and processing of speech have been linked to reading skills. In their work published in September 2014, the group established links between beat synchronization and speech processing in children who have not yet begun to read. This is very exciting work because children this young are not often looked at for deficits in language development.
To do this, the researchers placed children in groups based on how well they could synchronize beating a drum in rhythm with the teacher. It’s important to note that there were no differences in intelligence or vocabulary performance between the groups of synchronizers and non-synchronizers.
They recorded the brainwaves in response to specific syllable sounds like “ba” and “da”. They also looked at brainwaves when the syllable sounds were mixed in with background noise to see if the children could discriminate the syllables despite the noise. What they found was the children who could not synchronize well also did not perform as well on tests that measure abilities important for developing later reading and language language skills (for example, identifying rhyming words). They especially did not do well at distinguishing syllables played in background noise. The children who were able to follow the beat successfully were not only better at discriminating melodies and rhythms in music, but they were able to process syllable sounds more precisely and performed better on the multiple tests of language abilities.
Although this summary may sound somewhat simplistic, the methods were rigorous and the results highly significant. The results show beautifully that rhythmic ability is correlated with how precisely a child’s brain will decode speech syllables. The findings also strongly indicate that a preschooler’s ability to follow a beat will predict how advanced their developing language skills are; that less developed skills could predict future reading disabilities. To test this, they have set up a 5 year study to track the same children to see whether these early deficits predict reading and speech processing disorders.
What they find may mean that in the future, doctors and caregivers may have the means to assess the very young for risk of developing reading and related learning disabilities. And intervention (such as music games to improve rhythmic perception) could in theory be highly successful since at such a young age children’s brains are most malleable.
Our job as parents, teachers, and caregivers is to continue promoting awareness of the spectrum of hearing disorders, and emphasize how important it is to recognize and identify them early on. If we keep at it, then perhaps we won’t have to wait the typical 10 years it often takes for life science research to make it to the actual changes in the clinical and healthcare practices. For more information check out the resources below.
- Normal hearing is not enough to guarantee robust encoding of suprathreshold features important in everyday communication. Ruggles D, Bharadwaj H, Shinn-Cunningham BG Proc Natl Acad Sci U S A. 2011 Sep 13; 108(37):15516-21. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3174666/
- Hearing Impairments HIdden in Normal Listeners. Proc Natl Acad Sci U S A. Sep 27, 2011; 108(39): 16139–16140. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3182733/
- Woodruff Carr K, White-Schwoch T, Tierney A, Strait DL, Kraus N (2014). Beat synchronization predicts neural speech encoding and reading readiness in preschoolers. Proceedings of the National Academy of Sciences. doi: 10.1073/pnas.1406219111
- Kraus N, Slater J, Thompson E, Hornickel J, Strait D, Nicol T and White-Schwoch T (2014). Music enrichment programs improve the neural encoding of speech in at-risk children. Journal of Neuroscience. 34(36): 11913-11918. http://www.soc.northwestern.edu/brainvolts/