Visual attention can be considered from the perspective of distributed brain activity engendered by visual input. We propose that visual objects compete for representation in multiple brain systems, sensory and motor, cortical and subcortical. Competition is integrated, however, such that multiple systems converge, working on the different properties and action implications of a selected object. Top-down priming biases competition towards objects relevant to current behaviour. Recent single-unit studies have shown widespread suppression of ignored-object representations in extrastriate cortex, and patterns of spatial and nonspatial priming by task relevance. Human and monkey lesion studies have demonstrated the strong integration tendency of different spatial and nonspatial systems, also revealed in recent studies of normal behaviour. In many cases, no unitary brain system may be responsible for unitary cognitive events such as attention. Such events may emerge as distinct systems converge to work on common cognitive problems.