Afferent and efferent models of visual perceptual asymmetries: theoretical and empirical implications

Visual laterality studies are reviewed in the framework of an afferent hierarchical information-processing model. According to this model, the hemispheres are viewed as separate information-processing systems, each with its own components and resources, as well as a common pool of resources. Information is shared across interhemispheric pathways. The magnitude and direction of visual field differences are determined by two factors: the processing efficiency of the components in one hemisphere relative to the other and interhemispheric transmission to components that are functionally localized to only one hemisphere. Rules are derived for weighing the relative contribution of these to visual field differences. As designed, the model can accommodate dynamic features characteristic of competing efferent (attentional) models without sacrificing its basic structure. The model's adequacy and usefulness for interpreting and guiding research on normal and brain-damaged people is discussed.