There are two visual attention networks proposed by Maurizio Corbetta and Gordon L. Shulman (2002). These are top-down and bottom-up attention networks.One system, which includes parts of the intraparietal cortex and superior frontal cortex, is involved in preparing and applying goal-directed (top-down) selection for stimuli and responses. This system is also modulated by the detection of stimuli. The other system, which includes the temporoparietal cortex and inferior frontal cortex, and is largely lateralized to the right hemisphere, is not involved in top-down selection. Instead, this system is specialized for the detection of behaviourally relevant stimuli, particularly when they are salient or unexpected.There are also two ventral streams proposed by Melvyn A. Goodale and A. David Milner (1992). These are ventral stream and dorsal stream.We propose that the ventral stream of projections from the striate cortex to the inferotemporal cortex plays the major role in the perceptual identification of objects, while the dorsal stream projecting from the striate cortex to the posterior parietal region mediates the required sensorimotor transformations for visually guided actions directed at such objects.My question: What is the relationship between these two proposed networks? As in do they affect each other, or is one a preliminary network that occurs before the other? There have been studies on this but I am having difficulty making sense of them.Example: Visual streams and shifting attention (Brown 2009) http://www.sciencedirect.com/science/article/pii/S0079612309176045To gain insight into the relationship between M/dorsal and P/ventral activity and deploying visual attention, we used a covert cuing paradigm to manipulate attention while bottom-up and top-down perceptual stimulus variables created M/dorsal and P/ventral-biased conditions. One study examined the object advantage, where responses are faster for within-relative to equidistant between-object shifts of attention. Visual stream contributions to object- and spaced-based attention were revealed using psychophysically equiluminant conditions expected to reduce M/dorsal activity. Other studies investigating visual stream contributions to location-based inhibition of return (IOR) used IOR magnitude as an indicator of the ease or difficulty of deploying spatial attention. Greater IOR was found under P/ventral-biased conditions. Less IOR was found under M/dorsal-biased conditions. 
What is the relationship between visual attention network and visual stream (Two-streams hypothesis)?
neurobiology;vision;neural network;attention