Auditory Processing Disorders

Auditory Processing Disorders (APD)

The Scenario

  • Setting: Private practice in Johannesburg.

  • Characters: Audiologist, mother, and school-aged child.

  • Referred by: Teacher and parents.

  • Reason for referral:

    • Inconsistent response to auditory stimuli.

    • Difficulty listening in background noise.

    • Doesn't always pay attention or is daydreaming in class.

    • Difficulty following instructions.

    • Often "mishears" words.

Possible Explanations (and Why APD is Considered)

  • Conductive hearing loss (otitis media).

  • Unilateral hearing loss.

  • Sensorineural hearing loss.

  • Other factors: attention deficit, cognition, learning problems.

  • Crucially: The audiogram is NORMAL.

What We Need to Know

  • A definition of APD.

  • APD is "Subtle, yet significant" (Whitelaw, 2014).

  • Not a high incidence.

  • Importance of differential diagnosis: Can we separate APD from related disorders?

  • Review any relevant documents.

Top-Down vs. Bottom-Up Processing

  • Top-Down Processing Model:

    • Describes language processing.

    • Uses knowledge of language and the world to interpret the acoustic signal.

    • Focus is on language/semantic knowledge.

    • Speech-language pathologists' viewpoint.

  • Bottom-Up Processing Model:

    • Describes auditory processing.

    • Attends to individual components of the acoustic signal before linguistic interpretation.

    • Focus is on acoustic knowledge.

    • Audiologists' viewpoint.

Defining APD: A Lack of Consensus

  • "APD means different things to different people" (Jerger, 2009:10).

  • Helmer Mycklebust: "Inability to listen, to give sustained selected responses auditorially, is a characteristic of disturbed auditory perception…. " (Myklebust, 1954: 159).

  • Myklebust HR. Auditory disorders in children: A manual for differential diagnosis. New York: Grune & Stratton, 1954.

Current Schools of Thought (Wilson, 2014)

  • Audiological modality specificity.

  • Psycho-educational.

  • Impact on language acquisition and learning.

  • “Listening difficulties”.

  • Auditory attention.

Audiological Perspective (Medical Model)

  • Based on complaints, tests are administered and interpreted as normal or abnormal.

  • Aims to determine where the problem lies within the auditory system.

Psycho-Educational Perspective (Educational Model)

  • Based on the concept of primary (discrete) auditory abilities that can be tested.

  • Targets children for (C)AP evaluation due to assumed impact on learning and academic performance.

Language Acquisition and Learning Perspective

  • Problems in auditory perceptual processing could lead to problems in language acquisition and subsequent learning disabilities.

Modality Specificity Perspective (Wilson, 2014)

  • Considers three groups of individuals who perform poorly on (C)AP tests:

    • Specific perceptual problems processing information presented auditorily (APD in its "purist" form).

    • Auditory perceptual problems that coexist with other processing problems.

    • No auditory processing problems per se, but other problems with motivation, attention, memory, motor skills, etc. (McFarland and Cacace, 1995).

Auditory Attention Perspective

  • Suggests APD is primarily an auditory attention problem.

  • Clinical diagnosis, management, and further research should be based on this premise.

"Listening Difficulties" Perspective

  • Deliberately avoids defining APD.

  • Focuses on the diagnosis and management of listening difficulties (Dillon et al., 2012, p. 98).

Four Key Documents

  • American Speech-Language and Hearing Association (ASHA, 2005).

  • American Academy of Audiology (AAA, 2010).

  • British Society of Audiology (BSA, 2011; Moore et al. 2012).

  • NZ Guidelines on Auditory Processing Disorder (New Zealand Audiological Society, 2019).

  • Note: There is no consensus on presenting symptoms/behaviors of (C)APD.

  • We should focus on core symptom or symptoms that reflect and contribute to clinical presentation.

APD Definition (Keith, 1988)

  • "Any breakdown in the child’s auditory abilities that results in diminished learning through hearing, even though the hearing sensitivity is normal."

What APD Is NOT

  • A deficit in linguistic processing (as defined by speech-language pathologists).

  • A deficit in cognitive processing (as defined by psychologists).

  • Attention deficit hyperactivity disorder (ADHD).

So, What IS APD?

  • Deficits in the perceptual processing of auditory stimuli in the central nervous system and in the underlying neurobiological activity that gives rise to electrophysiological auditory potentials.

  • The predominant deficits characterizing CAPD manifest in the auditory modality.

Functional Problems (Chermak, 2018)

  • Difficulty understanding spoken language in competing message or noise backgrounds, in reverberant acoustic environments, or when rapidly presented.

  • Difficulty localizing the source of an auditory signal.

  • Difficulty with subtle intonation and prosodic cues.

  • Difficulty with similar sounding words.

  • Misunderstanding messages.

  • Responding inconsistently or inappropriately.

  • Frequently requesting repetitions.

  • Saying "what" and "huh" a lot.

  • Difficulty following complex auditory directions/commands.

  • Difficulty "hearing" on the phone.

  • Difficulty learning songs, nursery rhymes; poor musical/singing skills and/or music appreciation.

  • Difficulty learning foreign language or novel speech materials, especially technical language.

  • Taking longer to respond in oral communication situations.

  • Difficulty paying attention.

  • Easily distracted.

  • Academic difficulties: reading, spelling, and/or learning problems.

Common Characteristics

  • Majority are male.

  • Normal pure-tone hearing results.

  • Difficulty following oral directions.

  • Short auditory attention span / fatigue during auditory tasks.

  • Poor short-term and long-term memory.

  • Gives impression of not listening.

  • Difficulty listening in the presence of background sound.

  • Difficulty localizing sound.

  • Academic deficits, mild speech impairments.

  • Disruptive behaviors.

  • Frequent requests for verbal repetition.

  • History of Otitis Media.

Consequences of Late Diagnosis

  • Reading failure.

  • Academic failure.

  • Psychosocial problems.

  • Children with APD are at risk for:

    • Externalizing problems (e.g., aggression).

    • Internalizing problems (e.g., anxiety, depression).

    • Behavioral problems (e.g., Withdrawal).

    • Adaptive problems (e.g., social skills).

  • May require long-term remediation.

  • Increased cost and decreased benefit versus early identification and intervention.

Causes of CAPD in Children (Chermak, 2018)

1. Neurodevelopmental

  • Neuromaturational lag (20-30%) (likely due to delayed myelination and possibly auditory deprivation) (Bamiou, Musiek, & Luxon, 2001).

  • Neuromorphological (60-70%) (areas of brain failed to develop normally, underlying benign, diffuse neuroanatomic/neuromorphological abnormalities) (Musiek, Gollegly, & Ross, 1985; Boscariol et al., 2009, 2010, 2011).

  • Developmental abnormalities: Attention deficit hyperactivity disorders, dyslexia, language impairment, learning disability.

Important Note:

  • With neurological causes, there is:

    • No identifiable underlying neuropathology.

    • No lesion of the CANS.

    • No apparent prenatal or perinatal disease, injury, or exposure-related cause.

2. Acquired

  • Tumors of CANS.

  • Prematurity and low birth weight.

  • Extrinsic damage to the brain.

  • Cerebrovascular disorders.

  • Metabolic disorders.

  • Epilepsy (e.g., Landau Kleffner syndrome) (Bamiou, Musiek & Luxon, 2001).

Neuroscience Foundation for APD

  • Intrinsic redundancy: the pathway “spreads out” from the periphery to the cortex.

  • Processing in a hierarchical fashion (from one relay station to the next) and in parallel (within more than one channel at the same time).

  • The human auditory system is fully developed at birth; maturation/myelination continues long after (Sowell et al., 2003).

  • Myelination rate varies in the normal population and is sound-dependent.

  • Perinatal and childhood factors influence development of auditory processing, e.g., neurological risk factors (hyperbilirubinemia), conductive hearing loss, environmental deprivation

  • Genetic factors play a role in the etiology of APD

  • Brain plasticity

    • The brain has an inherent capacity for plasticity, i.e., the sensory representations may change in response to altered receptors, sensory environment, or use and learning.

    • Stimulation or deprivation of stimulation can alter the number of synapses and synaptic density of both the developing and the mature brain.

    • Plasticity is underpinned by neurochemical, physiological, structural changes and may also be associated with behavioral change (Musiek and Berge, 1998).

    • Three types of plasticity: developmental, compensatory (after lesions/damage), and learning-related (Scheich 1991).

    • Auditory training for APD could involve all three types of plasticity.

CANS Maturation and Myelination

  • CANS requires considerable time to mature, especially the corpus callosum, as well as intra-hemispheric connections.

  • Myelination may require 12-14 years before it approximates adult levels.

  • Some children’s CANS maturation may lag, causing their auditory processing abilities to lag; they may not be able to handle complex listening situations as well as children whose CANS are developing on track; in many cases, these children do “catch up,” often by the time they are teenagers.

  • Significantly increased latency and reduced amplitude of early components of the cortical auditory evoked potentials (AEPs) in children diagnosed with CAPD compared to same-age children without CAPD (Tomlin & Rance, 2016).

Disorders Often Co-Existing with APD

  • Peripheral hearing loss (conductive & sensory). Common in older clients and patients with TBI

  • Specific language impairment.

  • Learning disabilities.

  • Reading disorders.

  • ADHD.

  • Emotional & psychological disorders.

  • Developmental delay.

  • Seizure disorders.

  • Autism spectrum disorder.

Risk Factors: The Importance of Teamwork

  • Neurological dysfunction and disorders (doctors).

  • Neonatal risk factors.

  • Head injury.

  • Seizure disorders.

  • Chronic otitis media in preschool years (ENT).

  • Academic underachievement or failure (teachers and educational psychologists).

  • Family history of academic underachievement (parent).

  • Co-existing disorders (multiple professionals).

APD in Adults: Risk Factors and Clinical Indications (Hall, 2010)

  • Medical history.

  • Audiological history.

  • Communication complaints greater than expected by audiogram.

  • Deterioration in communication abilities with stable audiogram.

  • Unusually poor benefit from amplification.

Audiological Findings

  • Abnormality for crossed versus uncrossed acoustic reflexes.

  • Speech audiometry.

  • Very poor speech perception.

  • Rollover on PI-PB functions.

  • Problems with speech in noise.

  • Slow response time and processing speed.

  • Poor benefit from amplification.

APD in adults: Some of the etiologies(Hall, 2010)

  • Aging of the CANS

  • Combined peripheral and APD

  • Central auditory processing dysfunction with progressive peripheral hearing loss

  • Peripheral hearing loss with progressive central auditory dysfunction

  • Psychiatric / neurological disorders e.g.

  • Neoplasms

  • Cardiovascular disease

  • Dementias (Alxheimer’s disease)

  • Schizophrenia?

  • Parkinson's disease

  • Traumatic brain injury

  • Accidents

  • Gunshot wounds

  • Blasts and explosions