One of the single most important divisions in brain function is between the dorsal and ventral cortical streams. These two pathways have distinct specialities in terms of function, and both contribute to visual perception to varying degrees at a given point in time. It has traditionally been thought that the physical properties of the stimulus exclusively determines the relative contribution of these pathways to perception, for example, the ventral stream subserving object recognition and the dorsal stream the perception of object motion.
Here, however, I will discuss three cognitive factors that we have found to affect this balance: shifts in the location of the focus of attention, changing the size of the attended area, and the nature of motor interactions with objects. These results demonstrate that the relative balance of these systems in their contribution to perception is far more flexible than previously appreciated. Clinical implications of this flexibility (e.g., for disorders such as schizophrenia that implicate a dorsal-stream deficit) will be discussed.