Dyslexia is a specific learning difference that affects an individual’s ability to read and spell, despite normal intelligence and conventional instruction. It is neurological, resulting from underlying differences in how the brain processes language, particularly its sound components. Whether an individual can be dyslexic in one language but not another is complex, depending heavily on the specific linguistic structure of the languages involved. The underlying core deficit remains constant, but the visible reading difficulties change dramatically based on the writing system used.
The Role of Orthographic Depth
How dyslexia manifests across languages is dictated by orthographic depth. This concept refers to the consistency between a language’s written symbols (graphemes) and its spoken sounds (phonemes). Languages exist on a continuum from “shallow” to “deep” orthographies.
Shallow or transparent orthographies, such as Italian, Spanish, and Finnish, feature a highly consistent one-to-one mapping between letters and sounds. In these languages, a person with dyslexia typically learns to decode words accurately, but their reading is slow and lacks fluency. The difficulty presents as “speed dyslexia,” where the challenge is rapid, automatic word recognition.
Deep or opaque orthographies, like English and French, have an inconsistent letter-to-sound correspondence. Individuals with dyslexia struggle significantly with reading accuracy and decoding new words in these systems, often exhibiting a deficit in phonological awareness. The language’s inconsistency exacerbates the underlying phonological weakness, leading to more reading errors.
Subtypes of Dyslexia and Cognitive Processing
Dyslexia is not a single disorder; it presents as different subtypes linked to specific breakdowns in cognitive processing. The interaction between these cognitive deficits and a language’s orthographic depth determines the observed symptoms. The two most relevant subtypes are phonological and surface dyslexia.
Phonological dyslexia involves difficulty with phonological awareness—the ability to recognize and manipulate individual sounds in spoken language. Individuals with this subtype struggle to sound out unfamiliar words, especially non-words, because they cannot easily connect graphemes to phonemes. This deficit is pronounced in deep orthographies like English, where sound-to-symbol rules are complex.
Surface dyslexia is characterized by difficulty recognizing whole words by sight. These individuals rely heavily on sounding out every word, causing them to struggle with irregular words that do not follow standard phonetic rules, such as “yacht” or “colonel” in English. In a shallow orthography, a person with surface dyslexia might function well because most words are phonetically regular.
Manifestation Across Different Writing Systems
The contrast between language presentations becomes clearer when comparing alphabetic systems with non-alphabetic writing systems. The underlying neurological differences remain, but the required reading skills change, causing the symptoms to shift. This shows that the same person may appear impaired in one language but functional in another.
In logographic systems, such as Chinese, each character represents a whole word or concept, relying more on visual memory and morphology than on sound-to-letter mapping. Dyslexia in Chinese often manifests as difficulties with visuospatial processing and the rapid recall of complex characters, distinct from symptoms seen in alphabetic languages. Functional MRI studies show that reading Chinese uses different brain regions—more frontal areas—compared to reading English, which relies more on posterior regions.
Japanese uses a combination of writing systems: logographic Kanji and two syllabic scripts, Hiragana and Katakana. A person with dyslexia might struggle with the visual complexity and memorization demands of Kanji, but show fewer difficulties with the highly consistent, shallow syllabic scripts. This difference supports the idea that reading difficulty is tied to the demands of the specific writing system being processed.
Assessment and Intervention in Multilingual Individuals
The language-specific nature of dyslexia creates challenges for diagnosis and intervention in multilingual individuals. Clinicians must distinguish between a true learning disability and difficulties stemming from second language acquisition or lack of quality instruction. A key consideration is whether the individual has reading difficulties in their native language (L1) as well as their second language (L2).
Assessment must be conducted in the individual’s native or dominant language whenever possible, using culturally and linguistically appropriate tests. If a student with a transparent L1, such as Spanish, is only tested in a deep L2, like English, their reading accuracy might appear functional in L1, but their fluency indicates dyslexia. Intervention must be tailored to the specific orthography. For a deep orthography, instruction should focus on phonological awareness, while for a shallow orthography, the focus should be on building reading speed.