ABSTRACT
The bases of developmental dyslexia were explored using connectionist models. The behavioral literature suggests that there are two dyslexic subtypes: "phonological" dyslexia involves impairments in phonological knowledge whereas in "surface " dyslexia phonological knowledge is apparently intact and the deficit may instead reflect a more general developmental delay. We examined possible computational bases for these impairments within connectionist models of the mapping from spelling to sound. Phonological dyslexia was simulated by reducing the capacity of the models to represent this type of information. The surface pattern was simulated by reducing the number of hidden units. Performance of the models captured the major behavioral phenomena that distinguish the two subtypes. Phonological impairment has a greater impact on generalization (reading nonwords such as NUST); the hidden unit limitation has a greater impact on learning exception words such as PINT. More severe impairments produce mixed cases in which both nonwords and exceptions are impaired. Thus, the simulations capture the effects of different types and degrees of impairment within a major component of the reading system.
