An efferent or “motor-articulatory feedback” hypothesis for developmental dyslexia-phonological type is proposed from the Departments of Neurology and Psychiatry, University of Florida College of Medicine, Gainesville, FL. Most children learn to read by the alphabetic system, requiring phonological awareness and conversion of letters (graphemes) into speech sounds (phonemes). Most dyslexics have deficient phonological awareness and difficulty converting graphemes into phonemes. The left inferior frontal lobe is important in phonological reading, as suggested by patients with acquired lesions and PET studies of normal subjects. Dyslexic children are unable to perceive the position and movement of the articulatory apparatus (mouth, lips, tongue) during speech, impairing phonological awareness and conversion of graphemes to phonemes. Deficits in motor-articulatory programming or feedback may be related to this lack of awareness of articulators. [1]

COMMENT. Other current hypotheses for developmental dyslexia are 1) visual hypothesis, with dysfunction in the visual perception system, and 2) auditory hypothesis, with abnormalities in the rapid discrimination of low-contrast, complex sounds and associated speech and language disturbances.

A disconnection syndrome hypothesis for developmental dyslexia is proposed based on evidence from PET scanning studies conducted at the MRC Cognitive Development Unit, London, UK [2]. A rhyming and a short-term memory task with visually presented letters was used to study brain activity in 5 compensated adult developmental dyslexics. Brain regions normally activated in phonological processing were defective, and weak connections between anterior and posterior language areas are proposed.