What makes a graphic image a good visualization. Why is one visualization better than another. Why are 3D visualizations better than 2D visualizations in some cases but not others. How does the size of the display, color, contrast level, brightness or frame rate affect the usability of the visualization, and how do these 'physical' quantities affect the type and amount of information that can be extracted from the visualization by the user. These are just a few of the questions that a multi-disciplinary effort at the NRL are trying to answer. By combining visualization experts, physicist and cognitive scientists, awe are trying to understand the cognitive processes carried out in the minds of scientists at the time they perform a visual analysis of their data. The results from this project are being used for the design of visualization methodologies and basic cognitive work. In this paper, we present a general description of our project and a brief discussion of the results obtained trying to understand why 3D visualizations are sometimes better than 2D, as most of the attempts at studying this problem have resulted in theories that are either to vague or under-specified, or not informative across different contexts.