Auditory processing disorder and rarely known as King-Kopetzky syndrome or auditory disability with normal hearing (ADN) is an umbrella term for a variety of disorders that affect the way the brain processes auditoryinformation. Individuals with APD usually have normal structure and function of the outer, middle, and inner ear (peripheral hearing). However, they cannot process the information they hear in the same way as others do, which leads to difficulties in recognizing and interpreting sounds, especially the sounds composing speech. It is thought that these difficulties arise from dysfunction in the central nervous system.
The American Academy of Audiology notes that APD is diagnosed by difficulties in one or more auditory processes known to reflect the function of the central auditory nervous system. It can affect both children and adults. Although the actual prevalence is currently unknown, it has been estimated to be 2–7% in children in US and UK populations. APD can continue into adulthood. Cooper and Gates (1991) estimated the prevalence of adult APD to be 10 to 20%. It has been reported that males are twice as likely to be affected by the disorder as females, and that prevalence is higher in the elderly and increases with age.
Signs and symptoms
Many people experience problems with learning and day-to-day tasks with difficulties over time. Adults with this disorder can experience the signs and symptoms below:
- talk louder than necessary
- have trouble remembering a list or sequence
- often need words or sentences repeated
- have poor ability to memorize information learned by listening
- interpret words too literally
- need assistance hearing clearly in noisy environments
- rely on accommodation and modification strategies
- find or request a quiet work space away from others
- request written material when attending oral presentations
- ask for directions to be given one step at a time
Relation to attention deficit hyperactivity disorder
It has been discovered that APD and ADHD present overlapping symptoms. Below is a ranked order of behavioral symptoms that are most frequently observed in each disorder. Professionals evaluated the overlap of symptoms between the two disorders. The order below is of symptoms that are almost always observed. This chart proves that although the symptoms listed are different, it is easy to get confused between many of them.
|1. Inattentive||1. Difficult hearing in background noise|
|2. Distracted||2. Difficulty following oral instructions|
|3. Hyperactive||3. Poor listening skills|
|4. Fidgety or restless||4. Academic difficulties|
|5. Hasty or impulsive||5. Poor auditory association skills|
|6. Interrupts or intrudes||6. Distracted|
There is a high rate of co-occurrence between AD/HD and CAPD. An article published in 1994 showed that 84% of children with APD have confirmed or suspected ADHD. Co-occurrence between ADHD and APD is 41% for children with confirmed diagnosis of ADHD, and 43% for children suspected of having ADHD.
Acquired APD can be caused by any damage to or dysfunction of the central auditory nervous system and can cause auditory processing problems. For an overview of neurological aspects of APD, see Griffiths.
Some studies indicated an increased prevalence of a family history of hearing impairment in these patients. The pattern of results is suggestive that Auditory Processing Disorder may be related to conditions of autosomal dominant inheritance. The ability to listen to and comprehend multiple messages at the same time is a trait that is heavily influenced by our genes say federal researchers.
These “short circuits in the wiring” sometimes run in families or result from a difficult birth, just like any learning disability. Auditory processing disorder can be associated with conditions affected by genetic traits, such as various developmental disorders. Inheritance of Auditory Processing Disorder refers to whether the condition is inherited from your parents or “runs” in families. Central auditory processing disorder may be hereditary neurological traits from the mother or the father.
In the majority of cases of developmental APD, the cause is unknown. An exception is acquired epileptic aphasia or Landau-Kleffner syndrome, where a child’s development regresses, with language comprehension severely affected. The child is often thought to be deaf, but normal peripheral hearing is found. In other cases, suspected or known causes of APD in children include delay in myelin maturation, ectopic (misplaced) cells in the auditory cortical areas,or genetic predisposition.
In a family with autosomal dominant epilepsy, seizures which affected the left temporal lobe seemed to cause problems with auditory processing.In another extended family with a high rate of APD, genetic analysis showed a haplotype in chromosome 12 that fully co-segregated with language impairment.
Hearing begins in utero, but the central auditory system continues to develop for at least the first decade. There is considerable interest in the idea that disruption to hearing during a sensitive period may have long-term consequences for auditory development. One study showed thalamocortical connectivity in vitro was associated with a time sensitive developmental window and required a specific cell adhesion molecule (lcam5) for proper brain plasticity to occur.
This points to connectivity between the thalamus and cortex shortly after being able to hear (in vitro) as at least one critical period for auditory processing. Another study showed that rats reared in a single tone environment during critical periods of development had permanently impaired auditory processing. ‘Bad’ auditory experiences, such as temporary deafness by cochlear removal in rats leads to neuron shrinkage.
In a study looking at attention in APD patients, children with one ear blocked developed a strong right-ear advantage but were not able to modulate that advantage during directed-attention tasks.
In the 1980s and 1990s, there was considerable interest in the role of chronic Otitis media (middle ear disease or ‘glue ear’) in causing APD and related language and literacy problems. Otitis media with effusion is a very common childhood disease that causes a fluctuating conductive hearing loss, and there was concern this may disrupt auditory development if it occurred during a sensitive period.Consistent with this, in a sample of young children with chronic ear infections recruited from a hospital otolargyngology department, increased rates of auditory difficulties were found later in childhood.
However, this kind of study will suffer from sampling bias because children with otitis media will be more likely to be referred to hospital departments if they are experiencing developmental difficulties. Compared with hospital studies, epidemiological studies, which assesses a whole population for otitis media and then evaluate outcomes, have found much weaker evidence for long-term impacts of otitis media on language outcomes.
It seems that somatic anxiety (that is, physical symptoms of anxiety such as butterflies in the stomach or cotton mouth) and situations of stress may be determinants of speech-hearing disability.
Questionnaires can be used for the identification persons with possible auditory processing disorders, as these address common problems of listening. They can help in the decision for pursuing clinical evaluation. One of the most common listening problems is speech recognition in the presence of background noise.
According to the respondents who participated in a study by Neijenhuis, de Wit, and Luinge (2017), the following symptoms are characteristic in children with listening difficulties, and they are typically problematic with adolescents and adults. They include:
- Difficulty hearing in noise
- Auditory attention problems
- Better understanding in one on one situations
- Difficulties in noise localization
- Difficulties in remembering oral information
According to the New Zealand Guidelines on Auditory Processing Disorders (2017) a checklist of key symptoms of APD or comorbidities that can be used to identify individuals who should be referred for audiological and APD assessment includes, among others:
- Difficulty following spoken directions unless they are brief and simple
- Difficulty attending to and remembering spoken information
- Slowness in processing spoken information
- Difficulty understanding in the presence of other sounds
- Overwhelmed by complex or “busy” auditory environments e.g. classrooms, shopping malls
- Poor listening skills
- Insensitivity to tone of voice or other nuances of speech
- Acquired brain injury
- History of frequent or persistent middle ear disease (otitis media, ‘glue ear’).
- Difficulty with language, reading or spelling
- Suspicion or diagnosis of dyslexia
- Suspicion or diagnosis of language disorder or delay
The American Speech-Language-Hearing Association (ASHA) published “(Central) Auditory Processing Disorders” in January 2005 as an update to the “Central Auditory Processing: Current Status of Research and Implications for Clinical Practice (ASHA, 1996)”
The American Academy of Audiology has released more current practice guidelines related to the disorder. ASHA formally defines APA as “a difficulty in the efficiency and effectiveness by which the central nervous system (CNS) utilizes auditory information.”
In 2011, the British Society of Audiology published ‘best practice guidelines’.
Auditory processing disorder can be developmental or acquired. It may result from ear infections, head injuries or neurodevelopmental delays that affect processing of auditory information. This can include problems with: “…sound localization and lateralization ; auditory discrimination; auditory pattern recognition; temporal aspects of audition, including temporal integration, temporal discrimination (e.g., temporal gap detection), temporal ordering, and temporal masking; auditory performance in competing acoustic signals (including dichotic listening); and auditory performance with degraded acoustic signals”.
The Committee of UK Medical Professionals Steering the UK Auditory Processing Disorder Research Program have developed the following working definition of Auditory Processing Disorder: “APD results from impaired neural function and is characterized by poor recognition, discrimination, separation, grouping, localization, or ordering of speech sounds. It does not solely result from a deficit in general attention, language or other cognitive processes.”
Types of testing
1. The SCAN-C for children and SCAN-Afor adolescents and adults are the most common tools for screening and diagnosing APD in the USA. Both tests are standardized on a large number of subjects and include validation data on subjects with auditory processing disorders. The test batteries include screening tests: norm-based criterion-referenced scores; diagnostic tests: scaled scores, percentile ranks and ear advantage scores for all tests except the Gap Detection test.
The four tests include four subsets on which the subject scores are derived include: discrimination of monaurally presented single words against background noise (speech in noise), acoustically degraded single words (filtered words), dichotically presented single words and sentences.
2. Random Gap Detection Test (RGDT) is also a standardized test. It assesses an individual’s gap detection threshold of tones and white noise. The exam includes stimuli at four different frequencies (500, 1000, 2000, and 4000 Hz) and white noise clicks of 50 ms duration. It is a useful test because it provides an index of auditory temporal resolution. In children, an overall gap detection threshold greater than 20 ms means they have failed and may have an auditory processing disorder based on abnormal perception of sound in the time domain.
3. Gaps in Noise Test (GIN) also measures temporal resolution by testing the patient’s gap detection threshold in white noise.
4. Pitch Patterns Sequence Test (PPT) and Duration Patterns Sequence Test (DPT) measure auditory pattern identification. The PPS has s series of three tones presented at either of two pitches (high or low). Meanwhile, the DPS has a series of three tones that vary in duration rather than pitch (long or short). Patients are then asked to describe the pattern of pitches presented.
5. Masking Level Difference (MLD) at 500 Hz measures overlapping temporal processing, binaural processing, and low-redundancy by measuring the difference in threshold of an auditory stimulus when a masking noise is presented in and out of phase.