DOUBLE DISSOCIATION WITHOUT MODULARITY - EVIDENCE FROM CONNECTIONIST NEUROPSYCHOLOGY

Many theorists assume that the cognitive system is composed of a colle ction of encapsulated processing components or modules, each dedicated to performing a particular cognitive function. On this view, selectiv e impairments of cognitive tasks following brain damage, as evidenced by double dissociations, are naturally interpreted in terms of the los s of particular processing components. By contrast, the current invest igation examines in detail a double dissociation between concrete and abstract word reading after damage to a connectionist network that pro nounces words via meaning and yet has no separable components (Plaut a nd Shallice, 1993). The functional specialization in the network that gives rise to the double dissociation is not transparently related to the network's structure, as modular theories assume. Furthermore, a co nsideration of the distribution of effects across quantitatively equiv alent individual lesions in the network raises specific concerns about the interpretation of single-case studies. The findings underscore th e necessity of relating neuropsychological data to cognitive theories in the context of specific computational assumptions about how the cog nitive system operates normally and after damage.