auditory processing disorder

Detailing the Relationships Between Auditory Processing and Cognitive-Linguistic Abilities in Children

By Beula Magimairaj, Ph.D.

Children suspected to have or diagnosed with auditory processing disorder (APD) present with difficulty understanding speech despite typical-range peripheral hearing and typical intellectual abilities. Children with APD (also known as central auditory processing disorder, CAPD) may experience difficulties while listening in noise, discriminating speech and non-speech sounds, recognizing auditory patterns, identifying the location of a sound source, and processing time-related aspects of sound, such as rapid sound fluctuations or detecting short gaps between sounds. According to 2010 clinical practice guidelines by the American Academy of Audiology and a 2005 American Speech-Language-Hearing Association (ASHA) report, developmental APD is a unique clinical entity. According to ASHA, APD is not the result of cognitive or language deficits.

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In our July 2018 study in the journal Language Speech and Hearing Services in the Schools for its special issue on “working memory,” my coauthor and I present a novel framework for conceptualizing auditory processing abilities in school-age children. According to our framework, cognitive and linguistic factors are included along with auditory factors as potential sources of deficits that may contribute individually or in combination to cause listening difficulties in children.

We present empirical evidence from hearing, language, and cognitive science in explaining the relationships between children’s auditory processing abilities and cognitive abilities such as memory and attention. We also discuss studies that have identified auditory abilities that are unique and may benefit from assessment and intervention. Our unified framework is based on studies from typically developing children; those suspected to have APD, developmental language impairment, or attention deficit disorders; and models of attention and memory in children. In addition, the framework is based on what we know about the integrated functioning of the nervous system and evidence of multiple risk factors in developmental disorders. A schematic of this framework is shown here.

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In our publication, for example, we discuss how traditional APD diagnostic models show remarkable overlap with models of working memory (WM). WM refers to an active memory system that individuals use to hold and manipulate information in conscious awareness. Overlapping components among the models include verbal short-term memory capacity (auditory decoding and memory), integration of audiovisual information and information from long-term memory, and central executive functions such as attention and organization. Therefore, a deficit in the WM system can also potentially mimic the APD profile.

Similarly, auditory decoding (i.e., processing speech sounds), audiovisual integration, and organization abilities can influence language processing at various levels of complexity. For example, poor phonological (speech sound) processing abilities, such as those seen in some children with primary language impairment or dyslexia, could potentially lead to auditory processing profiles that correspond to APD. Auditory memory and auditory sequencing of spoken material are often challenging for children diagnosed with APD. These are the same integral functions attributed to the verbal short-term memory component of WM. Such observations are supported by the frequent co-occurrence of language impairment, APD, and attention deficit disorders.

Furthermore, it is important to note that cognitive-linguistic and auditory systems are highly interconnected in the nervous system. Therefore, heterogeneous profiles of children with listening difficulties may reflect a combination of deficits across these systems. This calls for a unified approach to model functional listening difficulties in children.

Given the overlap in developmental trajectories of auditory skills and WM abilities, the age at evaluation must be taken into account during assessment of auditory processing. The American Academy of Audiology does not recommend APD testing for children developmentally younger than age 7. Clinicians must therefore adhere to this recommendation to save time and resources for parents and children and to avoid misdiagnosis.

However, any significant listening difficulties noted in children at any age (especially at younger ages) must call for a speech-language evaluation, a peripheral hearing assessment, and cognitive assessment. This is because identification of deficits or areas of risk in language or cognitive processing triggers the consideration of cognitive-language enrichment opportunities for the children. Early enrichment of overall language knowledge and processing abilities (e.g., phonological/speech sound awareness, vocabulary) has the potential to improve children's functional communication abilities, especially when listening in complex auditory environments. 

Given the prominence of children's difficulty listening in complex auditory environments and emerging evidence suggesting a distinction of speech perception in noise and spatialized listening from other auditory and cognitive factors, listening training in spatialized noise appears to hold promise in terms of intervention. This needs to be systematically replicated across independent research studies. 

Other evidence-based implications discussed in our publication include improving auditory access using assistive listening devices (e.g., FM systems), using a hierarchical assessment model, or employing a multidisciplinary front-end screening of sensitive areas (with minimized overlap across audition, language, memory, and attention) prior to detailed assessments in needed areas.

Finally, we emphasize that prevention should be at the forefront. This calls for integrating auditory enrichment with meaningful activities such as musical experience, play, social interaction, and rich language experience beginning early in infancy while optimizing attention and memory load. While these approaches are not new, current research evidence on neuroplasticity makes a compelling case to promote auditory enrichment experiences in infants and young children.

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A 2015 Emerging Research Grants (ERG) scientist generously funded by the General Grand Chapter Royal Arch Masons International, Beula Magimairaj, Ph.D., is an assistant professor in the department of communication sciences and disorders at the University of Central Arkansas. Magimairaj’s related ERG research on working memory appears in the Journal of Communication Disorders, and she wrote about an earlier paper from her ERG grant in the Summer 2018 issue of Hearing Health.

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Accomplishments by ERG Alumni

By Elizabeth Crofts

Progress Investigating Potential Causes and Treatments of Ménière’s Disease

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Gail Ishiyama, M.D., a clinician-scientist who is a neurology associate professor at UCLA’s David Geffen School of Medicine, has been investigating balance disorders for nearly two decades and recently coauthored two studies on the topic. While not directly funded by HHF, Ishiyama is a 2016 Emerging Research Grants recipient and also received a Ménière’s Disease Grant in 2017.

Ishiyama and colleague’s December 2018 paper in the journal Brain Research investigated oxidative stress, which plays a large role in several inner ear diseases as well as in aging. Oxidative stress is an imbalance between the production of free radicals and antioxidant defenses. The gene responsible for reducing oxidative stress throughout the body is called nuclear factor (erythroid-derived 2)-like 2, or NRF2. Ishiyama’s study looked at the localization of NRF2 in the proteins in the cells of the human cochlea and vestibule. It was found that NRF2-immunoreactivity (IR) was localized in the organ of Corti of the cochlea. Additionally, it was observed that NRF2-IR decreases significantly in the cochlea of older individuals. The team postulates for future studies that modulation of NRF2 expression may protect from hearing loss that results from exposure to noise and ototoxic drugs.

In a January 2018 report in the journal Otology & Neurotology, Ishiyama and team researched endolymphatic hydrops (EH), a ballooning of the endolymphatic fluid system in the inner ear that is associated with Ménière’s disease. Symptoms include fluctuating hearing loss, as well as vertigo, tinnitus, and pressure in the ear.

For the study, patients with EH and vestibular schwannoma were tested to evaluate the clinical outcome of patients when EH is treated medically. Vestibular schwannoma, also known as acoustic neuroma, are benign tumors that grow in the vestibular system of the inner ear, which controls balance. Often when patients develop episodic vertigo spells and have a known diagnosis of vestibular schwannoma, surgeons recommend surgical intervention, as they attribute the symptoms to the vestibular schwannoma. However, a noninvasive treatment may hold promise. Through the use of high-resolution MRI scans, the researchers found that when EH coexists with vestibular schwannoma in a patient, and the patient also experiences vertigo spells, a medical treatment for EH—that is, the use of diuretics to relieve inner ear fluid buildup—may alleviate the vestibular symptoms.

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A 2016 ERG scientist funded by The Estate of Howard F. Schum, Gail Ishiyama, M.D., is an associate professor of neurology at UCLA’s David Geffen School of Medicine. She also received a 2017 Ménière’s Disease Grant.


New Insights Into Aging Effects on Speech Recognition

Age-related changes in perceptual organization have received less attention than other potential sources of decline in hearing ability. Perceptual organization is the process by which the auditory system interprets acoustic input from multiple sources, and creates an auditory scene. In daily life this is essential, because speech communication occurs in environments in which background sounds fluctuate and can mask the intended message.

Perceptual organization includes three interrelated auditory processes: glimpsing, speech segregation, and phonemic restoration. Glimpsing is the process of identifying recognizable fragments of speech and connecting them across gaps to create a coherent stream. Speech segregation refers to the process where the glimpses (speech fragments) are separated from background speech, to focus on a single target when the background includes multiple talkers. Phonemic restoration refers to the process of filling in missing information using prior knowledge of language, conversational context, and acoustic cues.

A July 2018 study in The Journal of the Acoustical Society of America by William J. Bologna, Au.D., Ph.D., Kenneth I. Vaden, Jr., Ph.D., Jayne B. Ahlstrom, M.S., and Judy R. Dubno, Ph.D., investigated these three components of perceptual organization to determine the extent to which their declines may be the source of increased difficulty in speech recognition with age. Younger and older adults with typical hearing listened to sentences interrupted with either silence or envelope-modulated noise, presented in quiet or with a competing talker.

As expected, older adults performed more poorly than younger adults across all speech conditions. The interaction between age and the duration of glimpses indicated that, compared with younger adults, older adults were less able to make efficient use of limited speech information to recognize keywords. There was an apparent decline in glimpsing, where interruptions in speech had a larger effect on the older adult group.

Older adults saw a greater improvement in speech recognition when envelope modulations were partially restored, leading to better continuity. This demonstrated that with age comes a poorer ability to resolve temporal distortions in the envelope. In speech segregation, the decline in performance with a competing talker was expected to be greater for older adults than younger adults, but this was not supported by the data.

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A 2015 Emerging Research Grants scientist, Kenneth I. Vaden, Jr., Ph.D., is a research assistant professor in the department of otolaryngology–head and neck surgery at the Medical University of South Carolina.

A 1986–88 ERG scientist, Judy R. Dubno, Ph.D., is a member of HHF’s Board of Directors. The study’s lead author, William Bologna, Au.D., Ph.D., is a postdoctoral research fellow at the National Center for Rehabilitative Auditory Research in Portland, Oregon.

A 2018 HHF intern, Author Elizabeth Crofts is a junior at Boston University studying biomedical engineering. For our continually updated list of published papers by ERG alumni, see hhf.org/erg-alumni.

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Sound Processing in Early Brain Regions

By Yishane Lee    

Standard hearing tests may not account for the difficulty some individuals have understanding speech, especially in noisy environments, even though the sounds are loud enough to hear. To better identify and treat these central auditory processing disorders that appear despite normal ear function, 2016 Emerging Research Grants (ERG) scientist Richard A. Felix II, Ph.D., and colleagues have been investigating how the brain processes complex sounds such as speech.

In the past, speech processing research has focused on higher-level brain regions like the auditory cortex, but there is strong evidence showing that lower-level subcortical areas may play a significant role in hearing disorders. In their paper “Subcortical Pathways: Toward a Better Understanding of Auditory Disorders,” published online in the journal Hearing Research on Jan. 31, 2018, Felix and team review studies that examine the auditory brainstem and midbrain and their functional effect on hearing ability.

The illustration shows the major inhibitory and excitatory, ascending and descending, neurotransmitter connections of subcortical pathways. The table lists features of auditory processing, with the contribution (or potential impairment) of each structure depicted with increasing strength represented by darker colors.

The illustration shows the major inhibitory and excitatory, ascending and descending, neurotransmitter connections of subcortical pathways. The table lists features of auditory processing, with the contribution (or potential impairment) of each structure depicted with increasing strength represented by darker colors.

Speech contains various acoustic hallmarks such as pitch, timbre, and gaps between starts and stops of sound energy that the brain uses to create distinct auditory “objects”—for example, listening to one voice among multiple talkers in a noisy room. Our brains extract these acoustic clues by decoding spectral, temporal, and spatial information in order to identify and understand complex sounds.

Studies of mammalian species show that these sound features are extracted at the level of the midbrain by nerve cells in a region called the inferior colliculus, and through the integration of multiple ascending (“bottom-up”) pathways: from inner ear hair cells to the auditory nerve; to the brainstem’s cochlear nucleus and superior olivary complex; to the midbrain’s inferior colliculus; to the forebrain’s thalamus; and to the auditory cortex.

For instance, several key functions of auditory processing previously attributed to the cortex, such as the selectivity of neurons to particular vocalizations, are now demonstrated in subcortical pathways. The cortex builds upon these coding strategies to produce typical hearing and communication abilities in most individuals.

Felix and team go on to detail auditory disorders that may result in large part from subcortical processing failures. Since neurotransmitters are important in the brain, including subcortical regions, an imbalance in these chemicals’ excitatory or inhibitory actions (as typically happens with age) can affect the ability to hear complex sounds.

Disruptions of bottom-up processing may lead to hearing difficulties that are not revealed using standard hearing tests. This includes auditory synaptopathy and auditory neuropathy (terms sometimes used interchangeably), also called “hidden hearing loss.” One concern with hidden hearing loss is that subcortical processing may be affected by noise levels previously thought to be relatively safe (as low as 80 decibels).

Likewise, central auditory processing disorders may be a result of abnormal top-down processing, leading to problems with selective attention and other hearing-related tasks.

The authors conclude, “Subcortical pathways represent early-stage processing on which sound perception is built; therefore problems with understanding complex sounds such as speech often have neural correlates of dysfunction in the auditory brainstem, midbrain, and thalamus.” The hope is that further study of animal models as well as human subjects will lead to tools to aid in the diagnosis and treatment of hearing disorders caused by problems with subcortical sound processing.

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Richard A. Felix II, Ph.D., is a postdoctoral researcher in the Hearing and Communications Lab at Washington State University Vancouver. A 2016 Emerging Research Grants recipient, he was generously funded by the General Grand Chapter Royal Masons International. Read more about Felix in “Meet the Researcher,” in the Summer 2017 issue of Hearing Health.


We need your help supporting innovative hearing and balance science through our Emerging Research Grants program. Please make a contribution today.

 
 
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Hearing—With Difficulty Understanding: Life With Auditory Processing Disorder

By Lauren McGrath

This April, Hearing Health Foundation (HHF) draws your attention to Auditory Processing Disorder (APD), a condition that causes impairments in sound localization—the ability to identify sound sources—and has been closely linked to autism. April 4 is recognized as APD Awareness Day in some regions of the U.S. and April is Autism Awareness Month nationwide.

APD occurs when the central nervous system has difficulty processing verbal or auditory information, specifically in noisy, social environments. Individuals with APD do not necessarily have a diagnosed hearing loss; in fact, many have normal audiogram results. With APD and typical hearing, the inner ear properly sends signals to the brain, but, once received, the brain fails to interpret and analyze these sounds accurately, resulting in jumbled messages.

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In the U.S., it is estimated five percent of school-age children, or 2.5 million children, have APD. Individuals with APD are often unable to hear sounds as words and have learning problems, including difficulty in reading, spelling, and language comprehension. It is vital to review the symptoms, demographics, and treatments of APD, should you suspect it in yourself or a loved one.

Individuals with APD have trouble distinguishing between words or syllables that sound alike (auditory discrimination) and recalling what they heard (poor auditory memory). They show delayed responses to verbal requests and instructions and will often ask someone to repeat what has been said. APD is commonly misdiagnosed as ADD/ADHD, dyslexia, or hearing loss.

Demographically, APD is a common secondary diagnosis for children with autism; most children diagnosed with autism have auditory processing disorders or auditory difficulties. HHF Emerging Research Grants (ERG) recipient Elizabeth McCullagh, Ph.D.’s 2017 published work in The Journal of Comparative Neurology examines the strong connection between Fragile X Syndrome (FXS), the most common genetic form of autism, and difficulties with sound localization.

Additionally, APD is prevalent in individuals with neurological problems, including those who have experienced head injuries or strokes. Older adults, who are more susceptible to some cognitive decline, are also at greater risk for APD.

Military veterans who have been repeatedly exposed to blasts are another community disproportionately affected by APD. An estimated 15% of all returning military personnel live with APD. HHF’s ERG recipient Edward Bartlett, Ph.D., explains that the changes to the central auditory system may account for the behavioral issues that veterans experience, such as problems with memory, learning, communication, and emotional regulation.

Retired U.S. Army Colonel John Dillard of HHF’s Board of Directors remarks, “It is truly unfortunate that our veterans, after making such honorable sacrifices, are forced to live with APD, often alongside tinnitus and/or hearing loss. I am hopeful that future scientific advancements will better the lives of veterans and all Americans.”

There are no cures for APD, but there are many treatments that aim to improve the effectiveness of everyday communication. These include environmental modifications, addressing functional deficits, and improving listening and spoken language comprehension. Pursuing treatment for APD as early as possible is imperative, McCullagh explains, because hearing is vital to social and educational interactions. “Those with APD often develop issues with language development, hearing in noise, and sound localization. Risks associated include not being able to participate in noisy environments which can often result in depression and anxiety.”

Much more research of APD is needed to improve the accuracy of methodologies for diagnosis and to determine the best interventions for each child or adult. Even though there are available strategies to treat APD, researchers, including those funded by HHF, largely through the generosity of the Royal Arch Masons Research Assistance, are hard at work finding alternative treatments that will improve the lives of those with APD.

We need your help supporting innovative hearing and balance science through our Emerging Research Grants program. Please make a contribution today.

 
 
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