Is auditory processing disorder just another name for dyslexia?


In 2015 the California legislature passed a dyslexia law, known as AB1369. Part of this new law requires schools to include phonological processing as one of the psychological processing disorders listed on the IEP documents under which a student can qualify for special education services. During the legislative process it was repeatedly stated by the opposition that this was unnecessary due to the fact that there was already the category of auditory processing.

LA-1223_LRIt became painfully obvious that there is confusion about the difference between an Auditory
Processing Disorder (APD), also known as Central Auditory Processing Disorder (C)APD, and dyslexia.

It is easy to understand why this confusion happens when we stop to think about how we describe dyslexia, but the difference is big and it is important to understand. Understanding this difference between (C)APD and dyslexia can save children from wasted time working on the wrong skills. But be aware, (C)APD has suffered the same fate as dyslexia, there are a lot of professionals who do not believe (C)APD is real. So, let’s dig in and see if we can come out with a clear explanation of the differences. Let’s start by investigating the definitions of (C)APD and dyslexia.

Central Auditory Processing Disorder (C)APD)

The American Speech-Language-Hearing Association (ASHA) and theAmerican Academy of Audiology define (C)APD the following way:

“(Central) auditory processing disorder [(C)APD] refers to difficulties in the processing of auditory information in the central nervous system (CNS) as demonstrated by poor performance in one or more of the following skills: 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.” (Central) Auditory Processing Disorders—The Role of the Audiologist

The definition very clearly delineates that (C)APD is the difficulty with processing sound. In addition, ASHA states:

“It (C)APD) cannot be contributed to higher-order language, cognitive, or related confounds (e.g. language disorder, language processing disorder,autism).” ASHA also clarified that: “Although abilities such as phonological awareness, attention to and memory for auditory information, auditory synthesis, comprehension and interpretation of auditorily presented information, and similar skills may be reliant on or associated with intact central auditory function, they are considered higher order cognitive-communicative and/or language-related functions and, thus, are not included in the definition of (C)AP.”

LA-615_LRThis caveat is extremely important in understanding the difference between (C)APD and dyslexia.Higher order language factors are factors that are involved in processing language, not sound. For example, there is a simulation that has participants try to write down information that is being spoken to them amongst a lot of background noise. This simulation is doing a great job simulating (C)APD, but not dyslexia.

Lastly, while Speech and Language Pathologists and other professionals can screen for dyslexia, according to the American Academy of Audiologists, only an audiologist can actually diagnose (C)APD. What is included in that battery of tests will be discussed below.


So, with that in mind, let’s take a look at the definition of dyslexia according to the International Dyslexia Association:

“Dyslexia is a specific learning disability that is neurobiological in origin. It is characterized by difficulties with accurate and/or fluent word recognition and by poor spelling and decoding abilities. These difficulties typically result from a deficit in the phonological component of language that is often unexpected in relation to other cognitive abilities and the provision of effective classroom instruction. Secondary consequences may include problems in reading comprehension and reduced reading experience that can impede growth of vocabulary and background knowledge.”

The definition of dyslexia is very clear stating that those with dyslexia may have difficulty manipulating language either verbally and/or when reading and spelling. Phonological processing is not difficulty hearing sounds, it is difficulty blending and manipulating phones and or phonemes.

Furthermore, many people with dyslexia actually have average to above average phonological skills, but they cannot apply that strength to the written word. This can manifest in slow reading and poor spelling, which is orthographic dyslexia. This has nothing to do with auditory processing. (See note about the misconception that spelling is completely dependent of hearing sounds).

Dyslexia is a higher cognitive function involving the language process. That is what sets it apart from (C)APD.

Identification of (C)APD and Dyslexia

Identification of (C)APD

How (C)APD and dyslexia are identified is another way to understand the differences between them. According to The Role of the Audiologist, when assessing for (C)APD the following skills are observed and measured:

  • Auditory discrimination tests: assess the ability to differentiate similar acoustic stimuli that differ in frequency, intensity, and/or temporal parameters (e.g., difference limens for frequency, intensity, and duration; psychophysical tuning curves; phoneme discrimination).
  • Auditory temporal processing and patterning tests: assess the ability to analyze acoustic events over time (e.g., sequencing and patterns, gap detection, fusion discrimination, integration, forward and backward masking).
  • Dichotic speech tests: assess the ability to separate (i.e., binaural separation) or integrate (i.e., binaural integration) disparate auditory stimuli presented to each ear simultaneously (e.g., dichotic CVs, digits, words, sentences).
  • Monaural low-redundancy speech tests: assess recognition of degraded speech stimuli presented to one ear at a time (e.g., filtered, time-altered, intensity-altered [e.g., performance intensity PI-PB functions]), speech-in-noise or speech-in-competition).
  • Binaural interaction tests: assess binaural (i.e., diotic) processes dependent on intensity or time differences of acoustic stimuli (e.g., masking level difference, localization, lateralization, fused image tracking).
  • Electroacoustic measures: recordings of acoustic signals from within the ear canal that are generated spontaneously or in response to acoustic stimuli (e.g., OAEs, acoustic reflex thresholds, acoustic reflex decay).
  • Electrophysiologic measures: recordings of electrical potentials that reflect synchronous activity generated by the CNS in response to a wide variety of acoustic events (e.g., ABR, middle latency response, 40 Hz response, steady-state evoked potentials, frequency following response, cortical event-related potentials [P1, N1, P2, P300], mismatch negativity, topographical mapping). The use of electrophysiologic measures may be particularly useful in cases in which behavioral procedures are not feasible (e.g., infants and very young children), when there is suspicion of frank neurologic disorder, when a confirmation of behavioral findings is needed, or when behavioral findings are inconclusive.

Identification of Dyslexia

It’s important for the student to first rule out any hearing issues. Then, the following list from Dyslexia Help at the University of Michigan outlines the areas to be tested to make a identification of dyslexia:

  • Language: A test of language that will give information about an individual’s receptive and expressive language abilities, language processing, morphological skills and pragmatic language skills.
  • Phonological awareness: The most distinguishing feature of dyslexia is poor phonological awareness, which manifests in an inability to identify and blend together individual phonemes in words.
  • Rapid naming/word fluency: Rapid naming is the ability to name symbols, words, or pictures rapidly. This discriminating skill is based on speed, not accuracy.
  • Reading fluency: Reading fluency is the combination of the score of the accuracy of reading and the rate (speed) of which one can read.
  • Reading comprehension: Reading comprehension is the understanding of the printed word.
  • Spelling: Spelling ability provides insight into other types of knowledge necessary for written communication. Poor spelling may reveal weaknesses in one or more of the following: Linguistic knowledge, Orthographic knowledge, Semantic knowledge, Morphological knowledge.
    *Note: this website also stated the following: “Poor spelling may also be a possible indicator of a hearing deficit or auditory processing disorder.” However, this is erroneous, since English orthography is not always a direct sound/symbol correlation. Therefore, if a student is spelling words the way they sound them out, that is not an auditory processing issue or a hearing issue, it is the student’s misunderstanding about how our written word in English differs from our spoken word. For example, a student who spells <try> as <triy> actually has superb auditory and phonological skills. This student is hearing all four phones in the spoken word but has failed to be taught that those four phones are represented by three phonemes. 
  • Writing: Deficiencies such as spelling errors, syntactic and semantic errors, morphological errors, omissions of words or word endings, and general incongruities may be present.


Comparison of Symptoms between (C)APD and Dyslexia

(C)APD Dyslexia
In school, children with APD may have difficulty with spelling, reading, and understanding information presented verbally in the classroom. In school, children with dyslexia may have difficulty with spelling, reading, and understanding information presented in print in the classroom.
Have trouble paying attention to and remembering information presentedorally Difficulty manipulating language bothverbally and in print
Need more time to process information Difficulty with spelling
Difficulty distinguishing between verbally presented sounds or words. They may hear clamp instead ofcamp. Difficulty with reading comprehension
Difficulty focusing when background noise is present. Difficulty with fluency
Have difficulty with reading, comprehension, spelling, and vocabulary. Difficulty with word problems
Difficulty remembering what was said to them
Difficulty following directions
Often responds to questions or comments with “what” or “huh?”


Now Hear This

Interestingly, after hours reading articles by audiologists and SLPs, I was struck by how they all referred to dyslexia LA-1287_LRas a co-existing (co-morbid) condition with (C)APD, this is important in understanding that they are two separate conditions that require different interventions. There were also many comments about the ambiguity and lack of consensus about (C)APD.

Now when someone asks you what is the difference between dyslexia and auditory processing you should be comfortable informing them that dyslexia is difficulty processing and manipulating language and auditory processing is difficulty processing sound. The differences have huge implications for how we help a child with either processing difficulty and the differences should not be taken lightly. A child with dyslexia should not be involved in interventions for auditory processing  and a child with auditory processing difficulties should not be involved in interventions for dyslexia, unless of course, that child has both. Now what about the difference between visual processing and dyslexia? Oh, that article is for another time and another day! Stay tuned.

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