On the interaction of selective attention and lexical knowledge: a connectionist account of neglect dyslexia.

Neglect dyslexia, a reading impairment acquired as a consequence of brain injury, is traditionally interpreted as a disturbance of selective attention. Patients with neglect dyslexia may ignore the left side of an open book, the beginning words of a line of text, or the beginning letters of a single word. These patients provide a rich but sometimes contradictory source of data regarding the locus of attentional selectivity. We have reconsidered the patient data within the framework of an existing connectionist model of word recognition and spatial attention. We show that the effects of damage to the model resemble the reading impairments observed in neglect dyslexia. In simulation experiments, we account for a broad spectrum of behaviors including the following: (1) when two noncontiguous stimuli are presented simultaneously, the contralesional stimulus is neglected (extinction); (2) explicit instructions to the patient can reduce the severity of neglect; (3) stimulus position in the visual field affects reading performance; (4) words are read much better than pronounceable nonwords; (5) the nature of error responses depends on the morphemic composition of the stimulus; and (6) extinction interacts with lexical knowledge (if two words are presented that form a compound, e.g., COW and BOY, the patient is more likely to report both than in a control condition, e.g., SUN and FLY). The convergence of findings from the neuropsychological research and the computational modeling sheds light on the role of attention in normal visuospatial processing, supporting a hybrid view of attentional selection that has properties of both early and late selection.