Dyslexia is a specific learning disability that is neurological in origin. It primarily affects a person’s ability to read and spell accurately and fluently. The core difficulty lies in processing written language, a complex task that relies on specialized brain networks. The dyslexic brain struggles with the underlying process of translating written symbols into sounds, which is the foundation of reading.
Debunking the Visual Myth
A widespread misconception is that dyslexia is a visual problem where letters appear to move, swim, or are seen backward. While some individuals report visual discomfort or “visual stress” when reading, the root cause is not a failure of the eyes. Standard eye examinations confirm that the eyes of a person with dyslexia function correctly; the difficulty originates in the brain.
The reported confusion, such as mixing up letters like ‘b’ and ‘d’ or transposing words like ‘was’ and ‘saw,’ results from the brain’s struggle to process and sequence symbols rapidly. These letter reversals are common in all young readers but persist much longer in those with dyslexia. The problem is primarily cognitive and linguistic, meaning specialized fonts or colored overlays do not address the core issue.
The Phonological Deficit
The scientific consensus points to a deficit in the phonological component of language as the primary cause of reading difficulty in dyslexia. Phonological awareness is the ability to recognize and manipulate the sound structure of spoken language. The core issue is the difficulty in mapping the written letter (grapheme) to its corresponding sound unit (phoneme).
This deficit impairs a person’s ability to decode words, which is the process of translating print into speech sounds. For example, a person with dyslexia struggles with phonemic awareness, the skill of breaking a word like “cat” into its individual sounds: /c/, /a/, /t/. They also have difficulty blending sounds back together to form a recognizable word, making “sounding out” unfamiliar words a slow and error-prone task.
Because of this breakdown in the sound-symbol connection, the brain fails to develop automatic word recognition. Each encounter with a word, even a common one, may require a laborious, sound-by-sound decoding effort. This fundamental language processing failure is what makes reading a struggle.
Neural Pathways in Dyslexia
Functional neuroimaging studies reveal that the brains of individuals with dyslexia show different patterns of activation during reading compared to non-impaired readers. Typical readers rely on a specialized “reading circuit” in the left hemisphere, which includes the temporo-parietal region and the occipito-temporal region. These areas are responsible for phonological processing and the rapid recognition of printed words.
In the dyslexic brain, these left-hemisphere areas often show reduced activation or “hypoactivity” during reading tasks. This diminished activity corresponds directly to the difficulty in linking visual symbols to their sounds. The brain attempts to compensate for this reduced engagement by activating alternative, less efficient pathways.
This compensation often involves increased activity in frontal regions, such as the left inferior frontal gyrus, which are associated with articulation and effortful, sound-based decoding. There is also an increased reliance on the right hemisphere, which is not optimized for the rapid, sequential processing required for fluent reading. This pattern illustrates the neural basis of the struggle to process written words efficiently.
Observable Reading Difficulties
Reading is often slow, hesitant, and labored, reflecting the constant, word-by-word effort of decoding. This lack of fluency means that cognitive resources are consumed by the act of reading itself, leaving fewer resources for comprehension.
Individuals may frequently guess words based on the initial letter or visual shape, leading to substitutions of words that look similar but have different meanings, such as reading “tired” for “tried.” They may also omit or substitute smaller connector words like “the” or “but.” The poor sound-symbol mapping also results in significant difficulties with spelling.