Superadditive effects of multiple lesions in a connectionist architecture:Implications for the neuropsychology of optic aphasia

Neuropsychological disorders have traditionally been understood in terms of a focal lesion to a single component of a cognitive architecture. Optic ap hasia (OA) defies explanation in this way. In OA, naming of visual stimuli is impaired in the absence of general Visual agnosia or anemia. OA has been explained by positing multiple semantic systems or multiple functional pat hways to visual naming. M. J. Farah (1990) instead sketched a parsimonious account based on multiple lesions-to pathways mapping visual input to seman tics and semantics to naming responses-and the assumption that the effects of the lesions are superadditive. The authors demonstrate superadditive eff ects of damage in a connectionist architecture and model other phenomena as sociated with OA. Multiple lesions with superadditivity provide a novel cla ss of explanations for neuropsychological deficits that previously seemed t o imply the existence of highly specialized processing components.