The Lost Children of Audiology: Rethinking APD, ANSD, and the Overlap No One Talks About

Introduction

This article is a follow-up to a previous piece that introduced the importance of ruling out Auditory Neuropathy Spectrum Disorder (ANSD) before diagnosing Auditory Processing Disorder (APD). That earlier article was meant as a starting point—an entry into a much larger conversation about how we define, test for, and support children with complex listening challenges.

Over the past seven years of clinical experience, a deeper and more nuanced question has emerged—one I didn’t feel could be addressed fully in that first article. What if some children don’t fit neatly into either category? What if there’s a gray area—an overlap between ANSD and APD—that hasn’t been clearly defined or widely acknowledged? In this article, I share what I’ve observed in clinical practice, particularly through the use of frequency compression and virtual audiology, and why I believe some children are being missed by our current testing models. These children don’t just challenge our definitions—they may be the key to redefining them.

What are APD and ANSD?

Auditory Processing Disorder (APD) and Auditory Neuropathy Spectrum Disorder (ANSD) are often described as two very different diagnoses. APD is considered a central disorder, where the brain has difficulty interpreting sounds, especially speech in complex environments. ANSD is a peripheral disorder, involving a disruption in how sound travels from the inner ear to the brain—usually due to problems in neural timing or signal transmission. On paper, the difference seems clear. But in real life, especially when working with children, the boundaries blur. Some children don’t fit neatly into one box or the other—and current testing may not be sensitive enough to detect the more subtle forms of either condition.

The Legacy of Dr. Charles Berlin

Much of what we know about ANSD comes from Dr. Charles “Chuck” Berlin, a brilliant auditory neuroscientist and compassionate educator. He helped define ANSD and taught that the cochlea might function normally, but the auditory nerve may not send a synchronized signal to the brain. This loss of timing creates distorted or jumbled speech perception, especially in noise. In a landmark study, Dr. Berlin and colleagues found that 85% of children with ANSD who received cochlear implants showed significant speech and language gains, while only 15% of those using hearing aids improved at the same level. The implant’s value wasn’t in making things louder—it was in restoring synchronized input to the brain. He also made it clear: very few children truly outgrow ANSD. While some show partial or fluctuating improvement, most benefit from a layered support plan that includes technology, visual language access, or both.

Testing ANSD: What We Can and Can’t See

Children with ANSD are usually identified with auditory brainstem response (ABR) testing. These tests measure how sound travels from the cochlea to the brainstem. In ANSD, those signals are often delayed or desynchronized. Acoustic reflexes are also used, and while they are not always absent, they are often elevated—something that must be interpreted carefully, especially in young children with small ear canals. Otoacoustic emissions (OAEs), though not used universally, are often included to verify that the outer hair cells of the cochlea are working normally. What makes this condition tricky is that most ABRs use broadband clicks. High-frequency dys-synchrony, which might account for some of the high frequency speech difficulties, can go entirely undetected.

While more advanced ABR protocols do exist—such as those using tone bursts or speech-like stimuli—they are rarely used outside of research or specialty clinics. Most audiologists use ABR primarily to estimate thresholds or rule out neurological disorders like tumors. ANSD is a relatively low-incidence condition, and the equipment to detect more nuanced cases is costly and rarely upgraded. Clinics purchase these machines once every decade or more, and often lack training or reimbursement for more specialized protocols. As a result, many children with mild or frequency-specific desynchrony are never identified. They pass newborn screens or basic ABRs, even though they clearly struggle with sound clarity, speech discrimination, and listening fatigue in real life.

Testing APD: Behavioral Tools and Blind Spots

Testing for APD focuses on how the brain interprets sound after it arrives. Since there’s no single APD test, audiologists use a battery of behavioral tasks. These might include dichotic listening tests, where different sounds are played into each ear to assess how the brain separates them; speech-in-noise tasks that simulate real-world listening; and temporal pattern tests that assess pitch and timing perception. But these tests are typically done in quiet rooms under ideal conditions. They don’t reflect real-world distractions. They also don’t measure listening fatigue, even though many children with APD-like symptoms struggle most after long periods of effort. Attention may be screened using basic measures, but not with the depth seen in formal ADHD evaluations. That means children with subtle executive functioning or attention difficulties may be misdiagnosed—or may pass APD tests even though they struggle daily in noisy classrooms. This is why test results must be interpreted alongside case history, parent reports, and real-life listening behavior.

A Blurry Middle Ground

Some children may technically “pass” both ABR and APD tests, yet still seem unable to hear clearly. These are often the kids who frustrate parents and educators—who can repeat words in quiet settings but fall apart in the real world. One child I worked with had been in speech therapy for seven years, mostly for persistent articulation issues involving high-frequency sounds. After being fit with frequency-compressed hearing aids, her speech improved almost immediately. Within two months, she no longer needed therapy. The difference wasn’t motivation or effort—it was access. Her brain simply hadn’t been hearing the sounds she was trying to produce.

The Power of Frequency Compression

Frequency compression, used in hearing aids like Phonak’s SoundRecover2, works by taking the highest pitches of speech—like the top octave of a piano—and squeezing them into a lower, more accessible range. This makes high-frequency sounds easier to perceive, especially for children who struggle with clarity, phoneme discrimination, or background noise. Many hearing aid manufacturers now offer some form of frequency lowering, but Phonak has led the research, especially in children. Unitron, which shares the same parent company (Sonova), offers similar technology. These tools are particularly helpful for children with suspected auditory desynchrony who don’t qualify for cochlear implants—but still need better access to the fine detail in speech. We’ve also seen frequency compression help children with hyperacusis or misophonia, not necessarily by improving clarity, but by making harsh sounds more tolerable. The reshaped signal seems to reduce reactivity and emotional overload in children who otherwise shut down in noisy spaces.

Visual Access Through Cued Speech

Dr. Berlin was also a strong proponent of Cued Speech, a simple visual system that uses hand shapes and positions near the face to show exactly what phonemes are being spoken. Cued Speech allows children to see the difference between sounds that look identical on the lips—like /b/ vs. /m/ or /t/ vs. /k/. For children with unreliable auditory input, cueing gives them consistent access to the phonological structure of language, supporting both speech and literacy. And the effect is neurological, not just functional. fMRI studies have shown that Deaf individuals process Cued Speech in the same auditory areas of the brain used for spoken language. This makes it one of the few visual supports that actively builds the brain’s speech processing network.

Virtual Practice and Clinical Truth

In all reality, my suggestion that frequency compression may reveal subtle high-frequency ANSD is not based on lab data or controlled studies—at least not yet. It’s based on clinical observation. As a private practitioner without access to university research labs or high-end diagnostic equipment, I don’t have the tools to run advanced ABR protocols or confirm neural synchrony with complex auditory stimuli. What I do have is treatment—and the ability to observe outcomes closely over time. And what I’m seeing, again and again, are children who were thought to have only APD, or dyslexia, or “mild hearing issues,” making significant functional gains once fitted with frequency-compressed hearing aids. These are not subtle improvements. They’re measurable changes in tolerance, clarity, language production, classroom engagement, and reading progress.

In addition, my role as a virtual audiologist—and quite possibly the only non-military provider in the U.S. working this way—places me well outside the traditional research landscape. I don’t work in a university clinic or hospital. I assess children in their real environments, often in quiet suburban homes, where they are more relaxed and functionally observable. There are real advantages to this model, especially for my neurodivergent clients, who often find clinical settings overwhelming. But it doesn’t produce journal-ready data. I know most research institutions wouldn’t collaborate with me, and they wouldn’t accept my data because I don’t use a booth or calibrate according to lab protocols. So I keep making notes. I keep watching what works. And I hope someone will eventually take a closer look.

Closing Reflection: The Lost Children of Audiology

I don’t know yet whether frequency compression is revealing a mild form of high-frequency ANSD, or whether it’s compensating for a form of APD we haven’t yet learned how to identify. I suspect it’s a combination of both—an overlap of subtle neural timing disruptions and central processing inefficiencies. It may even be part of the reason why I see more benefit from this approach than many others report. The children I work with often fall into the margins—those gray areas where traditional diagnoses fall short. And if nothing else, this is one more reminder that the Venn diagrams overlap, and that sometimes, the clearest answers come not from a test result, but from listening closely to what actually helps a child thrive.

Dr. Chuck Berlin was the father of ANSD identification and treatment. He wasn’t my father—but I would hope he’d be proud of what I’m trying to do with my work. Like him, I practice outside the lines of typical audiology, following function more than protocol, and looking for the kids no one quite knows what to do with. The ones who pass their hearing tests but still can’t understand. The ones who are told it’s attention or behavior or just a phase. I call them the lost children of audiology—not because they’re broken, but because our systems weren’t built to find them. And yet, when we listen carefully—when we offer access to sound, to language, and to support that fits—they show us exactly who they are.

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References

Barone, P., Deguine, O., & Truy, E. (2010). Cued Speech and cochlear implant: A study of audiovisual integration by functional MRI. Hearing Research, 260(1–2), 151–158. https://doi.org/10.1016/j.heares.2009.12.004

Berlin, C. I., Morlet, T. G., & Hood, L. J. (2010). Auditory neuropathy/dyssynchrony: Its diagnosis and management. Pediatric Clinics of North America, 57(6), 1303–1316. https://doi.org/10.1016/j.pcl.2010.08.013

Rance, G., Beer, D. E., Cone-Wesson, B., Shepherd, R. K., Dowell, R. C., King, A. M., et al. (2002). Clinical findings for a group of infants and young children with auditory neuropathy. Ear and Hearing, 23(3), 234–248. https://doi.org/10.1097/00003446-200206000-00006

Phonak. (2016). SoundRecover2 – Adaptive frequency compression. https://www.phonak.com/content/dam/celum/phonak/master-assets/en/documents/evidence/hearing-aids/insight-sound-recover2-season1-2016-210x297-v2.00-028-1512-02-gb.pdf