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Guest post: Auditory processing disorder – a cause of language problems or an incidental finding?

30 Mar, 2011

ResearchBlogging.org
What causes a child’s language problems? Is it a problem with hearing? A problem with the brain’s interpretation of speech? Is it genetic? Specialists sometimes diagnose ‘Auditory Processing Disorder’ but the term itself is a complicated affair, writes Dorothy Bishop.

Five-year-old Charlie doesn’t speak very clearly, and doesn’t always understand what people are saying. His speech and language therapist says he has a specific language impairment, but his mum thinks he may be deaf. His family doctor refers him to an audiologist, who gives a hearing test and shows that Charlie can detect sounds just as well as other children. The audiologist suggests, however, that he may have an auditory processing disorder, or APD. The family doctor, however, has never heard of APD and is not sure whether it means that Charlie needs a different kind of treatment.

Parents are understandably confused when their child receives multiple diagnoses, some of which may not be found in paediatric textbooks. Use of the APD diagnostic label shows massive geographical variation. The diagnosis is common in the USA and Australia, and rare in the UK. I’ve commented elsewhere on the commercial pressures that may affect the variable use of the term. Here, I want to explain how scientists can go about trying to pinpoint the source of a child’s difficulties.

The field of APD is full of controversy, but let’s start with a point that most people will agree on, namely there’s more to auditory perception than is measured in an audiogram.

An audiogram is the result of a standard hearing test where you are played loud and soft sounds and have to indicate when you can hear them. Poor hearing is often the result of a problem in the peripheral auditory system, i.e. the middle or inner ear. But as well as being able to detect soft sounds: you also have to tell different sounds apart and recognise sounds (see Figure 1). Just as you can be colour-blind despite 20/20 vision, it’s possible to have problems with discrimination and identification of sounds despite having a normal audiogram.

Figure 1.  Different stages involved in processing sounds in the brain (see Bishop, D. V. M. (1997). Uncommon Understanding: Development and Disorders of Language Comprehension in Children. Hove: Psychology Press).

Figure 1. Different stages involved in processing sounds in the brain (see Bishop, D. V. M. (1997). Uncommon Understanding: Development and Disorders of Language Comprehension in Children. Hove: Psychology Press).

Problems of this kind originate in the brain rather than the ear. The ear’s role in hearing is to turn a sound wave into a neural signal. This is then transmitted up the auditory nerve to different brain regions that decode the signal. Studies of adult neurological patients have shown that if certain brain regions are damaged then it can be difficult to interpret what is heard, even though you know a sound occurred. We also know from studies of animals that there are cells in the auditory regions of the brain that respond to specific sound features, such as pitch, duration or spatial location. So it seems entirely plausible that there may be children who have developmental abnormalities of the central auditory system that affect their ability to perceive particular sound features, with consequent knock-on effects on language development.

So why is this controversial? One problem is that nobody can agree on how APD should be defined. From time to time professional groups get together to try and sort out agreed criteria for diagnosis, but this has not led to consensus, perhaps because there is only a slender research basis. One key issue noted by Moore (2006) is that existing tests tend to use speech stimuli to diagnose APD. This leads to ambiguity because poor auditory performance can arise from lack of language skills rather than the other way around. For instance, Japanese listeners often have difficulty distinguishing ‘r’ and ‘l’ sounds, not because there is anything wrong with their hearing, but because their language does not make this distinction. And English speakers do just as poorly when required to distinguish sound contrasts that our own language does not have, such as length contrasts that are used in Finnish.

The importance of language knowledge was made clear in a study that used an American speech-based APD test with children in the UK. They did far worse than American children when tested using speech stimuli delivered in an American accent (Dawes & Bishop, 2007). For this reason, researchers in the UK have developed tests of auditory processing for children that involve sounds such as tones, rather than speech (Moore et al., 2010).

But even this may not sort out the chicken and egg problem of whether an auditory problem causes language difficulties or vice versa. Figure 2 shows possible relationships between these deficits.

Figure 2. Difference explanations for a correlation between auditory processing deficit and poor language skills

Figure 2. Difference explanations for a correlation between auditory processing deficit and poor language skills

Interpretation A is often assumed if auditory deficits are found in a child with language problem, i.e. people assume that the auditory problem has caused the language difficulties. That is a reasonable enough account, given that the child needs to hear language properly to learn it. However, the opposite relation could also explain the results. Suppose children’s language difficulties arose for quite different reasons e.g. problems in interpreting word meanings, so they take longer to learn new words. This might lead them to be less attentive to auditory features, just because they are less skilled interpreters of speech. Or consider the case of listening to a foreign language, where the listener has perfectly normal auditory processing but limited knowledge of the language. Compared to a native Finnish speaker, you or I may have more difficulty hearing differences in the length of two tones just because length differences are important for distinguishing speech sounds in Finnish but not in English. Thus, if we find a correlation between auditory deficit and language deficit, it can be difficult to distinguish interpretation A and B.

To make matters even more complicated, there is also interpretation C, where the co-occurrence of auditory and language deficits does not involve any causal link between the two; instead both deficits arise as the consequence of another factor. What might such a factor be? Well, to take just one example, some children have delayed maturation of certain brain regions. This could impact on a range of skills. Or another example would be a genetic abnormality that affects several different aspects of development.

These different interpretations have important implications for intervention. If interpretation A is correct, then it would make sense to train the child’s auditory skills, as this could have beneficial effects on language. However, if B or C are correct, then auditory training would not be effective.

To disentangle these alternatives we need converging evidence from several sources.  One body of research takes children with language problems as a starting point. It explores their ability to hear different types of sound contrast to establish which, if any, auditory deficits are associated with language difficulties. This might seem like a fairly straightforward question, yet after some 40 years of research there is still considerable disagreement. There are problems both with the evidence itself and with the interpretation of that evidence.

Part of the difficulty in this field arises because young children are not very happy at sitting and making judgements about to hard-to-distinguish sounds for minutes on end. Suppose we want to find out if a child can hear differences between sounds that differ in pitch. Ideally, we want to establish a threshold level at which the difference is just noticeable. So we could play children pairs of sounds and ask them to judge if they are the same or different.

The problem is that the average 7-year-old lasts about two minutes on such a task before asking ‘how much more is there?’ and looking bored. Rather like a parent driving off on holiday with a child in the back seat, the experimenter has the unfortunate task of explaining that there are only another hundred trials to go. Some of my work in this area has been focused on the theoretically unexciting but practically important task of inventing auditory ‘games’ that the child will cheerfully play for long enough to give a sensible auditory discrimination threshold (see Fig 3). Even so, if we find that children with language difficulties do less well than typically-developing children, it can be hard to certain that we have identified a real auditory problem rather than poorer attention or concentration.

Figure 3. Screenshot of auditory discrimination game for children. Each dinosaur makes a noise at it jumps on its box, and the child has to identify which sound is different from the sound made by the central dinosaur. Correct responses are rewarded with cheerful noises and icons on the screen.

Figure 3. Screenshot of auditory discrimination game for children. Each dinosaur makes a noise at it jumps on its box, and the child has to identify which sound is different from the sound made by the central dinosaur. Correct responses are rewarded with cheerful noises and icons on the screen.

Because of this difficulty, I have become interested in alternative methods that do not require the child to attend and explicitly respond to stimuli. Using electrophysiological recording from electrodes situated on the scalp it is possible to measure the minute electrical discharges that occur in the brain when a sound is presented to the ear. By averaging over many stimulus presentations, we can detect a distinct kind of waveform representing activity over time in underlying auditory cortex. Of particular interest is a method whereby we compare the brain responses to different auditory stimuli, such as tones of different pitch or the sounds ‘ba’ and ‘da’.

Unfortunately, although this sounds neat, results are not always consistent from one study to another (Bishop, 2007). In a recent study we found, however, that whereas children with language problems had normal brainwaves at a point that corresponded to stimulus discrimination, they showed abnormalities at a later stage that appeared to reflect stimulus identification (Bishop et al., 2010). This was evident in both school-aged and teenaged children, and was seen for non-speech as well as speech stimuli.

There is a widespread tendency to assume that if you find differences in the brain responses of children with language impairment compared with a control group, that this means you have found the origin of children’s language difficulties.  However, the same logic applies as with the behavioural results (Figure 2): we need to consider interpretations B and C as well as A.

Currently, the field tends to be polarised between those who think auditory deficits are an important cause of children’s language problems (interpretation A), and those who think they are either the consequence of language problems (interpretation B) or an incidental finding (interpretation C). My current view based on research to date? I think auditory processing problems may play a contributory role in causing language and literacy problems, but they are not the cause.

There are several reasons for this conclusion. First, attempts to remediate language difficulties by auditory training have been largely disappointing (Loo et al, 2010). Second, there is mounting evidence that genetic differences between children play an important role in the cause of children’s language difficulties, but this is not so for the auditory deficits that can accompany language problems (Bishop, 2006). The ability to identify and remember the sounds of speech seems to be a specific skill that is crucial for language learning and that can be disrupted in some children, even when their nonlinguistic auditory processing is entirely normal.

In sum, I would be reluctant to throw out the baby with the bathwater and deny any role of auditory impairment in causing problems with language learning, but the evidence to date suggests we should be cautious about using the term ‘auditory processing disorder’. Very often, difficulties in doing auditory tasks reflect the child’s poor language or attentional skills, rather than a primary perceptual cause of their difficulties. An important conclusion from research in this area is that we need more multidisciplinary working between audiology and other professions concerned with developmental disorders to get a fuller picture of how hearing and language problems are related (see Dawes & Bishop, 2009).

Dorothy Bishop

Dorothy Bishop is Professor of Developmental Neuropsychology and a Wellcome Trust Principal Research Fellow at the Department of Experimental Psychology at the University of Oxford. She blogs at BishopBlog and tweets as @deevybee.

References

  • Bishop, D. (2006). Developmental cognitive genetics: How psychology can inform genetics and vice versa The Quarterly Journal of Experimental Psychology, 59 (7), 1153-1168 DOI: 10.1080/17470210500489372
  • Bishop, D. (2007). Using mismatch negativity to study central auditory processing in developmental language and literacy impairments: Where are we, and where should we be going? Psychological Bulletin, 133 (4), 651-672 DOI: 10.1037/0033-2909.133.4.651
  • Bishop DV, Hardiman MJ, & Barry JG (2010). Lower-frequency event-related desynchronization: a signature of late mismatch responses to sounds, which is reduced or absent in children with specific language impairment. The Journal of neuroscience : the official journal of the Society for Neuroscience, 30 (46), 15578-84 PMID: 21084613
  • Dawes P, & Bishop DV (2007). The SCAN-C in testing for auditory processing disorder in a sample of British children. International journal of audiology, 46 (12), 780-6 PMID: 18049967
  • Dawes P, & Bishop D (2009). Auditory processing disorder in relation to developmental disorders of language, communication and attention: a review and critique. International journal of language & communication disorders / Royal College of Speech & Language Therapists, 44 (4), 440-65 PMID: 19925352
  • Ferguson MA, Hall RL, Riley A, & Moore DR (2011). Communication, listening, cognitive and speech perception skills in children with auditory processing disorder (APD) or Specific Language Impairment (SLI). Journal of speech, language, and hearing research : JSLHR, 54 (1), 211-27 PMID: 20689032
  • Loo JH, Bamiou DE, Campbell N, & Luxon LM (2010). Computer-based auditory training (CBAT): benefits for children with language- and reading-related learning difficulties. Developmental medicine and child neurology, 52 (8), 708-17 PMID: 20370814
  • Moore, D. (2006). Auditory processing disorder (APD): Definition, diagnosis, neural basis, and intervention Audiological Medicine, 4 (1), 4-11 DOI: 10.1080/16513860600568573
  • Moore DR, Ferguson MA, Edmondson-Jones AM, Ratib S, & Riley A (2010). Nature of auditory processing disorder in children. Pediatrics, 126 (2) PMID: 20660546
  • 9 Comments leave one →
    1. 30 Mar, 2011 8:22 pm

      se puede estudiar por medio de la sensaciones o ademanes que produce el rostro el sistema nervioso esta pegado como una red que sometiendolo a sonidos agudos o suaves analizando los gestos a movimientos del niño en cuanto los movimientos diarios el sistema nervioso se comunica por impulsos que producen movimientos en los musculos del rostro hay observar la varivilidad de estos musculos o el movimiento de los ojos

    2. RAMACHANDRA PARARAJASEGARAM permalink
      18 Apr, 2011 3:46 pm

      The paper unravels the complexity of the hearing process. What is sometimes equated with hearing impairment as determined by audiometry may ignore other qualities of sound somewhat akin to say colour vision or contrast sensitivity as applied to vision.

    3. 27 Dec, 2012 9:24 am

      Yes, it must be really hard to unravel the cause. Meanwhile, for persons affected by it who are trying to manage their lives and relationships as adults with a hidden disability, I have pulled together an overview about the experience and coping strategies for people who interact with the affected person, “What is Auditory Processing Disorder (APD)?” — comments are welcome at: http://wp.me/p30k25-2

    4. 10 Feb, 2013 3:51 am

      Thank you for the article.

      My son was diagnosis with APD in Ca. We have are now living in TX. He reeives only support in the classroom and is doing fine in school. Going into 9th grade in the fall. The high school year requires to be on a college bound track he needs to take a foreign language. I think that is a huge mistake. It take him 3X as long to do work then a regular student to understand what is going on. My suggestion is since most college accept American Sign Language as a foreign language then we should go that way. He could learn to read lips and facial expresion better (took pragmatic speech in grades (1-4). Would love to know what you think?

    5. Louise permalink
      12 Jul, 2014 12:43 am

      Awesome post. You have thoroughly explained this condition and I think that any parent that reads it will be able to see if they have this issue with their child. So many kids get wrongly diagnosed with ADD. Louise.

    6. Marisa Galea permalink
      21 Jul, 2014 9:32 am

      Hi, is this condition different from Auditory Neuropathy? My son is 2 years old, he hasn’t developed any speech yet and about 4 weeks ago he had a grommet insertion in both ears. Afterwards we did an ABR test that came out abnormal. After grommets I am noticing several responses from his hearing. We have also an MRI scheduled next week. The doctor suggested a CI implant but I have to be sure if my child is hearing or not. Please help.

      • 21 Jul, 2014 5:15 pm

        We are not able to give any sort of clinical advice I’m afraid. The best thing to do is speak to your doctor about the options and ask them about anything that you are unsure of.
        Best wishes.

    7. 25 Feb, 2016 7:31 am

      I’ve recently started taking meditation more seriously and now meditate everyday. I have a super active mind which would sometimes distract me while I’m painting. Meditation has helped me to be present and focus while I paint. It’s an amazing feeling to let your ego go while you paint and just flow through each movement. https://www.mental-waves-for-happiness.com/product/secrets-of-zen-meditation-zen-music

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