Auditory Perceptual Disorders

Abstract

Auditory perceptual disorders, also called auditory processing disorders, are a type of cognition disorder, conditions in which the brain struggles to make sense of sound although the ears work normally and the audiogram is clear. The difficulty lies in the central auditory nervous system and surfaces as trouble understanding speech in noise, telling similar sounds apart, locating a source, or following rapid acoustic patterns. This article sets out what separates a central disorder from ordinary hearing loss, the auditory processes a diagnosis is built from, the battery used to probe them, and the controversy over how the disorder should be defined and whether it is specific to hearing. Three interactive demonstrations let the reader follow speech through noise, compare the ears in a dichotic task, and see how the diagnostic cutoff decides who counts as a case.

Keywords: auditory processing disorder, central auditory processing, speech in noise

An auditory perceptual disorder is a difficulty in making sense of sound that cannot be explained by the ear: the peripheral hearing organ works, the audiogram is normal, and yet the listener cannot reliably discriminate, localise, or follow what is heard (Bamiou et al., 2001). In the Medical Subject Headings vocabulary the condition is catalogued, as its name states, as a disorder of auditory perception, and it is filed among the cognition disorders, because the failure is one of processing rather than of sensation. In clinical classification it is coded in the tenth revision of the International Classification of Diseases as central auditory processing disorder, H93.25, and the eleventh revision places it among diseases of the ear (Iliadou et al., 2017). The distinction is the whole of the matter: hearing loss is a problem of getting sound in, while an auditory processing disorder is a problem of what the brain does with sound once it has arrived (Griffiths, 2002). The sections below set out that central locus, the auditory processes a diagnosis is built from, the test battery that probes them, the unusually sharp controversy over how the disorder should be defined, and what is known about its development, overlap with other conditions, and management.

A Disorder of Processing, Not of Hearing

The category exists to name a paradox that clinicians meet often: a person, frequently a child, who plainly cannot cope with sound in ordinary settings yet passes a standard hearing test. The audiogram measures the softest tones the ear can detect, and it probes the periphery, the cochlea and the auditory nerve. An auditory perceptual disorder lives past that point, in the central auditory nervous system, the brainstem, midbrain, thalamic, and cortical machinery that turns a detected sound into a recognised one (Bamiou et al., 2001). Because detection is intact, the deficit does not show up as a raised threshold; it shows up as failure on the harder task of making sense of sound that is rapid, degraded, competing, or spatially complex. The clearest way to see what the disorder is, and is not, is to see where along the auditory pathway it falls, which Figure 1 sets out: the audiogram tests only the first stretch, while the disorder occupies the rest.

Central, Not Peripheral

If the ear is working, why is listening so hard? The answer is that recognising sound is a computation, not a reception, and the computation can fail while reception succeeds. Understanding speech in a noisy room, for instance, requires pulling a target voice out of a competing background, a feat of auditory scene analysis that the modern account frames as the formation and tracking of an auditory object, a coherent perceptual whole assembled from the acoustic mixture (Griffiths & Warren, 2004). When that machinery is compromised, quiet speech in a quiet room may be perfectly clear while the same speech against background noise becomes unintelligible, even though every individual sound is loud enough to detect. This is why the defining complaint is so specific: not that sound is too soft, but that it will not resolve when the listening conditions are hard. The demonstration below models that signature directly, plotting how the share of words a listener catches climbs with the signal-to-noise ratio, and how the whole curve shifts so that an affected listener needs a quieter background to reach the same score that a typical listener reaches in more noise.

The Auditory Processes a Diagnosis Is Built From

Because the disorder is defined by what the brain does with sound, a diagnosis has to name which auditory processes fail, and the field works from an explicit inventory of them rather than from a single global measure (Bamiou et al., 2001). The processes span the discrimination of similar sounds, the localisation of a source in space, the resolution and ordering of sounds in time, the integration and separation of what arrives at the two ears, the recognition of acoustic patterns, and the extraction of a message from a degraded or competing signal. Temporal processing is central among them, because speech unfolds fast and the auditory system must resolve gaps and order events on a scale of milliseconds; the ability to recognise the pattern of a sequence of tones, for example, is a sensitive marker of central function and is disturbed by lesions of the auditory cortex and the pathways that join the hemispheres (Musiek et al., 1990). Table 1 sets out the principal processes with an everyday sign of difficulty in each.

Table 1

Auditory Processes Probed in a Central Auditory Assessment

Note. The processes are the components a central auditory assessment probes so that a diagnosis names where the difficulty falls rather than asserting a global failure of hearing (Bamiou et al., 2001; Musiek et al., 1990).

Assessment and Diagnosis

Since no single test captures the disorder, assessment uses a battery, each test stressing a different process under conditions the everyday audiogram never imposes (Bamiou et al., 2001). Dichotic tasks, in which different words or digits are presented to the two ears at the same moment, probe binaural integration and reveal how the ears divide the labour of listening. Degraded-speech tests, using filtered or time-compressed words, probe auditory closure, the ability to fill in a partial signal. Competing-speech and speech-in-noise tests probe figure-ground separation, and temporal tests such as gap detection and pattern recognition probe the fine timing on which speech depends. The dichotic task is especially informative about the central locus, because the two ears are not equal: the right ear reaches the language-dominant left hemisphere by a direct route, while the left-ear signal must cross the corpus callosum, so a listener with weak interhemispheric transfer shows a disproportionate left-ear deficit against a normal audiogram. The demonstration below models that right-ear advantage and shows the ear gap widen as transfer weakens.

The Diagnostic Controversy

Few diagnoses in this field are as contested as this one, and the disagreement is not about detail but about foundations. One line of criticism concerns modality specificity: if the deficit is truly a disorder of hearing, it should show up on auditory tasks but not on comparable tasks in vision, yet many children who fail an auditory battery also struggle with attention, language, and memory in ways that are not confined to sound, which suggests the problem may be a more general one that merely surfaces in the auditory tests (Cacace & McFarland, 2005). A second line concerns overlap: the profile of a child diagnosed with an auditory processing disorder is frequently indistinguishable from that of a child with a developmental language disorder, a reading disorder, or an attention disorder, and the same child often meets criteria for several at once, raising the question of whether the auditory label names a distinct condition or re-describes a shared one (Dawes & Bishop, 2009). A third, more practical line concerns the criteria themselves. Because a case is defined by failing a cutoff on some number of tests in a battery, the diagnosis is only as stable as those thresholds, and studies applying different but reasonable criteria to the same children find that the rate of diagnosis swings dramatically (Wilson & Arnott, 2013). Even the boundaries of the concept have been called a riddle, on the grounds that a disorder defined by exclusion and by test performance, rather than by a known mechanism, risks being whatever the tests happen to measure (Rosen, 2005). The demonstration below makes the criterion problem concrete: it shows how many genuinely typical listeners a battery would label as cases, purely by chance, as the cutoff is loosened.

Development, Comorbidity, and Management

Most cases are developmental, identified in school-aged children who struggle to listen in noisy classrooms, though the disorder can also be acquired, following a stroke, a tumour, or a degenerative process that damages the central auditory pathways (Griffiths, 2002). Systematic review of the developmental form finds that its characteristics are heterogeneous and that no single test profile defines it, which is part of why the diagnosis remains difficult to pin down (de Wit et al., 2016). Comorbidity is the rule rather than the exception, with substantial overlap between auditory processing difficulties and disorders of language and reading, so assessment increasingly aims to characterise a child across domains rather than to award a single label (Sharma et al., 2009). Large-scale study of children referred for auditory processing problems has suggested that their difficulties often reflect more general cognitive and attentional factors as much as a dedicated auditory deficit, reinforcing the case for a broad assessment (Moore et al., 2010). Management follows the same logic and works on several fronts at once: environmental measures that improve the signal, such as reducing classroom noise or using a remote microphone; direct auditory training, which draws on the auditory system's capacity for plasticity of the kind seen when musical training sharpens the neural encoding of sound (Kraus & Chandrasekaran, 2010), though the evidence that such training remediates the disorder itself remains limited (de Wit et al., 2016); and support aimed at the language, attention, and learning difficulties that so often accompany it. A European consensus has argued that progress depends on agreed definitions and shared protocols, without which studies cannot be compared and the controversy cannot be resolved (Iliadou et al., 2017).

Worked Example

The criterion demonstration above turns on a piece of arithmetic worth doing by hand, because it shows how a diagnosis can be manufactured out of ordinary variation. Suppose a battery has six independent tests, and a case is defined as scoring below a chosen cutoff on at least two of them. Now consider a genuinely typical listener, one with no disorder, whose score on each test is a standard normal deviate. If the cutoff is set at one standard deviation below the mean, the chance of falling below it on any one test is the normal tail probability, about 0.159. The chance this typical listener fails at least two of the six is one minus the chance of failing none minus the chance of failing exactly one. The chance of failing none is the probability of passing all six, that is 0.841 raised to the sixth power, about 0.355. The chance of failing exactly one is six, for the six tests that could be the failed one, times 0.159 for that failure, times 0.841 to the fifth power for the other five passes, about 0.401. So the chance of failing at least two is one minus 0.355 minus 0.401, about 0.244. Nearly a quarter of perfectly typical listeners would be labelled as cases by this rule, through chance alone. Tighten the cutoff to two standard deviations below the mean, where the per-test tail probability is about 0.023, and the same calculation gives a chance of about 0.007, well under one in a hundred. The tests have not changed and the listeners have not changed; only the criterion has, and it moved the false-positive rate from about one in four to under one in a hundred. This calculation idealises the battery as six independent tests; real subtests are correlated, so the exact figures are not a property of any particular test set but an illustration of a mechanism that shows up empirically, where different but reasonable criteria applied to the same children yield markedly different rates of diagnosis (Wilson & Arnott, 2013). This is why the choice of criteria is not a technicality but a determinant of who is diagnosed.

Discussion

The auditory perceptual disorders occupy an unusually revealing position in cognitive psychology, because they force a distinction the intact mind lets us ignore: the difference between sensing a stimulus and making sense of it. That a person can detect every sound yet fail to understand speech in noise is a natural demonstration that perception is an active construction layered on top of sensation, and that the construction has its own machinery which can break on its own (Griffiths & Warren, 2004). The category also serves as a cautionary study in how a disorder is defined. A condition specified by test performance rather than by mechanism, and diagnosed by cutoffs on a battery, inherits all the statistical hazards of that design, most sharply the way a lenient criterion converts normal variation into a diagnosis (Wilson & Arnott, 2013). And the heavy overlap with language, attention, and reading disorders keeps alive a genuinely open question about whether the auditory processing disorder is a distinct entity or one face of a broader developmental difficulty (Dawes & Bishop, 2009). None of this makes the listening difficulty less real for the people who have it; it makes the label a matter of live scientific dispute, and it is more honest to present the disorder as contested than to present it as settled.

Common Misconceptions

An auditory processing disorder is a kind of hearing loss.

It is not. Hearing loss is a peripheral problem of detecting sound, and it shows on the audiogram; an auditory processing disorder is a central problem of interpreting sound, and the audiogram is typically normal (Bamiou et al., 2001). The two can coexist, but confusing them misdirects both assessment and management (Griffiths, 2002).

A single failed test settles the diagnosis.

No single test defines the disorder, and a case rests on a pattern across a battery. Because chance alone drops some scores below any cutoff, a rule that requires too few failures labels many typical listeners, which is why the criteria are chosen with the false-positive rate in mind (Wilson & Arnott, 2013; Cacace & McFarland, 2005).

The diagnosis is a clearly bounded, hearing-specific entity.

Its boundaries are genuinely disputed. The profile overlaps heavily with language, attention, and reading disorders, and there is real debate about whether the deficit is specific to hearing or a more general difficulty that surfaces in auditory tests (Dawes & Bishop, 2009; Moore et al., 2010).

Glossary

Auditory closure.

The ability to recognise a word or message from a partial or degraded acoustic signal, tested with filtered or time-compressed speech.

Auditory discrimination.

The capacity to tell apart sounds that differ subtly in frequency, intensity, or timing, including the speech sounds that distinguish words.

Auditory object.

A coherent perceptual whole, such as a single voice, assembled by the brain from a mixture of overlapping sounds; forming and tracking it underlies listening in noise.

Auditory processing disorder.

A central difficulty in making sense of sound despite normal hearing sensitivity; the clinical term for an auditory perceptual disorder.

Binaural integration.

The combining of the different signals arriving at the two ears into a single percept; probed by dichotic tasks that present competing items to each ear.

Central auditory nervous system.

The brainstem, midbrain, thalamic, and cortical structures that process sound after the ear and auditory nerve have detected it; the site of an auditory perceptual disorder.

Dichotic listening.

A task in which different sounds are presented to the two ears at the same instant and the listener reports both, used to assess how the ears share the work of listening.

Gap detection.

A measure of temporal resolution: the shortest silent gap in a sound that a listener can detect, a marker of the fine timing on which speech depends.

Interhemispheric transfer.

The passage of auditory information across the corpus callosum between the two hemispheres; weak transfer produces a disproportionate left-ear deficit in dichotic tasks.

Masking.

The reduction in audibility or intelligibility of one sound caused by the presence of another, such as background noise obscuring speech.

Modality specificity.

The requirement that a disorder said to be auditory should impair auditory tasks specifically, rather than tasks in any sense; a central point of dispute in the diagnosis.

Pure-tone audiogram.

The standard hearing test that charts the softest tones a person can detect across frequencies; it measures the periphery and is typically normal in an auditory processing disorder.

Right-ear advantage.

The usual superiority of the right ear in reporting dichotic speech, arising because its route to the language-dominant left hemisphere is more direct.

Sound localisation.

The judgment of where a sound comes from, computed largely from differences in timing and level between the two ears.

Speech reception threshold.

The signal-to-noise ratio, or sound level, at which a listener correctly reports half of the presented speech; a summary of listening difficulty.

Temporal processing.

The resolution, ordering, and integration of sounds in time, on a scale of milliseconds, essential for perceiving rapid speech and its rhythm.

Key Researchers

Dorothy V. M. Bishop. Emeritus Professor of Developmental Neuropsychology in the Department of Experimental Psychology at the University of Oxford; her work on developmental language disorders includes an influential critique of the auditory processing disorder construct and its overlap with language and attention. Faculty Page - ORCID - Google Scholar - Wikipedia

Timothy D. Griffiths. Professor of Cognitive Neurology at Newcastle University and the Wellcome Centre for Human Neuroimaging at UCL; his work on auditory objects and central auditory pathologies underpins the modern account of how the brain builds and tracks sound. Faculty Page - ORCID

David R. Moore. Auditory neuroscientist at Cincinnati Children's Hospital Medical Center and the University of Manchester; his large-scale studies of children referred for auditory processing problems reshaped the debate over how much of the difficulty is specifically auditory. Faculty Page - ORCID - Google Scholar

Frank E. Musiek. Professor Emeritus of Speech, Language, and Hearing Sciences at the University of Arizona; a leading figure in the assessment of central auditory processing, he developed and validated many of the behavioural tests the diagnosis relies on. Faculty Page - ORCID

Frequently Asked Questions

What is an auditory perceptual disorder?
It is a difficulty in making sense of sound that arises in the brain rather than the ear, so that a person with normal hearing sensitivity still cannot reliably discriminate, localise, or follow what is heard, especially in demanding conditions (Bamiou et al., 2001). It is also called an auditory processing disorder, and it is classed as a disorder of auditory perception rather than as a hearing loss.

How is it different from hearing loss?
Hearing loss is a peripheral problem of detecting sound and shows up on the audiogram as raised thresholds, whereas an auditory processing disorder is a central problem of interpreting sound and usually leaves the audiogram normal (Griffiths, 2002). The two can occur together, but they are distinct and call for different responses.

What are the signs of an auditory processing disorder?
The hallmark is difficulty understanding speech when background noise or other voices compete, along with trouble discriminating similar sounds, locating a source, following rapid speech, and integrating what the two ears receive (Bamiou et al., 2001). These difficulties appear despite normal pure-tone hearing.

How is it diagnosed?
Diagnosis uses a battery of behavioural tests, including dichotic listening, degraded and competing speech, and temporal tasks such as gap detection and pattern recognition, with a case defined by performance falling below cutoffs on the battery (Musiek et al., 1990). Because the criteria strongly affect the outcome, careful assessment across domains is important (Wilson & Arnott, 2013).

Why is the diagnosis controversial?
The profile overlaps heavily with language, attention, and reading disorders, and critics question whether the deficit is specific to hearing or a more general difficulty that surfaces in auditory tests (Cacace & McFarland, 2005; Dawes & Bishop, 2009). Different but reasonable diagnostic criteria also yield very different rates, so the boundaries of the condition remain disputed (Rosen, 2005).

Does an auditory processing disorder cause reading or language problems?
It frequently occurs alongside language and reading disorders, and the overlap is substantial, but co-occurrence is not the same as cause, and the direction of any relationship is not settled (Sharma et al., 2009). Many children who fail auditory tests also show broader cognitive and attentional differences (Moore et al., 2010).

Can it be treated?
Management works on several fronts: improving the signal with quieter settings or a remote microphone, direct auditory training that draws on the brain's plasticity, and support for the language, attention, and learning difficulties that often accompany it (Kraus & Chandrasekaran, 2010). No single treatment resolves it, and the evidence base is still developing (de Wit et al., 2016).

Is an auditory processing disorder a lifelong condition?
The developmental form is identified in childhood and can change as the auditory system matures and as training and support take effect, though difficulties may persist (Iliadou et al., 2017). An acquired form, following injury or disease of the central auditory pathways, follows the course of its underlying cause (Griffiths, 2002).

Support Organizations

Organizations that provide information, assessment guidance, and professional standards for auditory processing and hearing.

References