Dyslexia is a poorly understood condition that is generally considered to be a learning disorder. Its root cause remains unknown, and the theories regarding it reflect this uncertainty, though there is believed to be a genetic link and structural differences in the brains of dyslexics. It is primarily a disorder that affects processing of written language. Psychological theories regarding dyslexia are discussed below, though it should be noted that some theories rely heavily on research modalities most appropriate to scientific psychology rather than cognitive psychology.
Evolutionary Hypothesis
The Evolutionary Hypothesis essentially suggests that reading is such a new feature in human development that it could be considered an abnormal act. As such, the differences between an excellent reader and a poor reader are just natural variations in brains that have just recently--in evolutionary terms--picked up the skill of reading.
Magnocellular Theory
Magnocellular Theory attempts to provide an explanation for the entire constellation of possible symptoms of dyslexia. It holds that all of the symptoms stem from a deficit in the magnocellular systems of brain. Although magnocellular systems are typically discussed in connection with visual data, the theory holds that they are tasked with processing large volumes of coarse sensory data from all areas.
The Phonological Hypothesis
The Phonological Hypothesis holds that there is an impairment in the ability of dyslexics to store, retrieve and represent phonemes (the basic units of speech). As reading is often taught using phonetic methods, an inability to tie phonemes to graphemes (the basic units of writing) will hinder the dyslexic's ability to understand the written word.
Cerebellar Theory
The Cerebellar Theory asserts that there is impairment of the cerebellum, which is responsible for motor control and automation of overlearned tasks (i.e. reading). As poor motor control could affect articulation, it could negatively affect phonological representation. This could in turn hinder the dyslexic's ability to form appropriate connections between phonemes and graphemes.
Perceptual Visual-Noise Exclusion Hypothesis
The Perceptual Visual-Noise Exclusion Hypothesis asserts that the symptoms dyslexics suffer stem from a underdeveloped ability to filter perceptual data appropriately. In essence, the dyslexic cannot distinguish between important visual/auditory stimulus and non-important visual/auditory stimulus.
Tags: holds that, asserts that, auditory stimulus, basic units, Cerebellar Theory, dyslexic ability, Evolutionary Hypothesis