The neurological bases of dyslexia are now well established and reflected in current definitions of the
condition. For example, the International Dyslexia Association (formerly the Orton Dyslexia Society)
published the following definition of dyslexia:
"Dyslexia is a neurologically-based, often familial disorder which interferes with the acquisition of
language. Varying in degrees of severity, it is manifested by difficulties in receptive and expressive
language, including phonological processing, in reading, writing, spelling, handwriting and
sometimes arithmetic. Dyslexia is not the result of lack of motivation, sensory impairment, inadequate
instructional or environmental opportunities, but may occur together with these conditions. Although
dyslexia is life-long, individuals with dyslexia frequently respond successfully to timely and
appropriate intervention" (Orton Dyslexia Society, 1994).