Effects of Word Abstractness in a Connectionist Model of Deep Dyslexia

Deep dyslexics are patients with neurological damage who exhibit a variety of symptoms in oral reading, including semantic, visual and morphological effects in their errors, a part-of-speech effect, and better performance on concrete than abstract words. Extending work by Hinton & Shallice (1991), we develop a recurrent connectionist network that pronounces both concrete and abstract words via their semantics, defined so that abstract words have fewer semantic features. The behavior of this network under a variety of “lesions” reproduces the main effects of abstractness on deep dyslexic reading: better correct performance for concrete words, a tendency for error responses to be more concrete than stimuli, and a higher proportion of visual errors in response to abstract words. Surprisingly, severe damage within the semantic system yields better performance on abstract words, reminiscent of CAV, the single, enigmatic patient with “concrete word dyslexia.”