Dyslexia and APD. What’s the link?

Like other neurodivergent conditions, Dyslexia can also be correlated with auditory processing difficulties. But what’s the exact link between those conditions anyway? First, let’s read about each one of them…

Dyslexia is a specific learning difficulty that affects primarily reading and spelling abilities in a way that is not explained by overall cognitive abilities or environmental factors (such as teaching methods). Those difficulties are most often related to phonological processing difficulties. Phonological processing is the ability to recognise and manipulate the sounds of spoken language; for example, the ability to break words into individual sounds (phonemes) and manipulate them. This ability is essential when it comes to decoding (reading) and encoding (spelling) words, as it enables us to combine sounds or syllables to form words.

Research has shown that, in a subgroup of children with Dyslexia, those problems related to phonological processing have an auditory origin. This is because, to recognise and manipulate those speech sounds, it is essential to hear and discriminate them very well so we can properly associate them with the corresponding letter. This group of children, on the other hand, would struggle to discriminate general acoustic elements of short duration that vary over time, including stop consonants (e.g., /p/, /t/, /k/, /d/) as they are characterised by their rapid sound changes. As a consequence, they would develop an unstable mental representation of those sounds, leading to problems in building and consolidating accurate phoneme (sound)-grapheme (letter) associations.

This auditory processing difficulty, known as auditory temporal processing, is observed through non-verbal tests, also referred to as auditory processing tests, which encompass different frequencies (pitch) or silent gaps with varying durations.  Those tests are included in the Auditory Processing Assessment, enabling clinicians to discuss specific management options if this issue is detected.

As mentioned above, this auditory processing difficulty is found in only a subgroup of children with Dyslexia and does not explain all phonological processing issues.

The picture below summarises the correlation explained above:

References:

Fitch RH, Miller S, Tallal P. Neurobiology of speech perception. Annu Rev Neurosci. 1997;20:331-53. doi: 10.1146/annurev.neuro.20.1.331.

Ahissar M, Protopapas A, Reid M, Merzenich MM. Auditory processing parallels reading abilities in adults. Proc Natl Acad Sci U S A. 2000 Jun 6;97(12):6832-7.

Gori M, Ober KM, Tinelli F, Coubard OA. Temporal representation impairment in developmental dyslexia for unisensory and multisensory stimuli. Dev Sci. 2020 Sep;23(5):e12977.

Wang LC, Yang HM. Temporal Processing Development in Chinese Primary School-Aged Children With Dyslexia. J Learn Disabil. 2018 May/Jun;51(3):302-312

Galaburda AM. Animal models of developmental dyslexia. Front Neurosci. 2022 Nov 14;16:981801