Dyslexia

Abstract

Dyslexia is a disorder characterised by difficulty in learning to read that cannot be attributed to secondary organic, mechanical or social circumstances. In other words, a child fails to learn to read at an age‐appropriate rate, irrespective of intelligence level, education or other neurological deficits. Notably, developmental dyslexia – which is the focus of this article – is distinct from acquired dyslexia, which occurs due to brain trauma. Numerous sensory and cognitive deficits contribute to dyslexia, including difficulties with auditory processing of speech sounds, visual processing and working memory. Current research is aimed at understanding the neurobiological cause of these cognitive deficits. Key Concepts Dyslexia is a universal and persistent form of low literacy in which a child fails to learn to read at an age‐appropriate rate. It is found across languages and is not associated with intelligence, age, education or other neurological deficits. Symptoms of dyslexia and their severity can vary significantly from one individual to the next. People with dyslexia have been found to have Impaired phonological processing – that is, a decreased perceptual sensitivity to sound‐segments in language. Difficulties with short‐term memory. Impaired visual processing. Spelling difficulties. Phonological dyslexia refers to difficulties in sounding words out and making phonological manipulations. Surface dyslexia refers to difficulties in developing and accessing a lexicon, that is a mental representation of words. Dyslexia is often confused with visual stress – the symptoms of which include words moving when attempting to read, shimmering or disappearing, words looking like they were carved into the page, lines or rivers through the text, and preferring to read under very low light levels. The exact aetiology of dyslexia is unknown; however, evidence indicates deficits in magnocellular‐dorsal stream processing in the visual domain and impaired brainwave function in the auditory domain. Several genetic mutations have also been identified in dyslexia. Current remedial interventions for dyslexia are educational and are aimed at improving cognitive deficits. Current research is aimed at identifying the neurobiological basis of dyslexia to aid the development of a treatment that targets the underlying neurobiological cause of dyslexia.