System control—the issuing of commands—is a critical, but largely unexplored task in 3D user interfaces (3DUIs) for immersive virtual environments (IVEs). System control techniques are normally encompassed by complex interfaces that define how these interaction techniques fit together, which we call system control interfaces (SCIs). Creating a testbed to evaluate these SCIs would be beneficial to researchers and would lead to guidelines for choosing a SCI for particular application scenarios. Unfortunately, a major problem in creating such a testbed is the lack of a standard task sequence—the order of operations in a system control task. In this research, we identify various task sequences, such as the Action-Object and Object- Action task sequences, and evaluate the effects that these sequences have on usability, in hopes of establishing a standard task sequence. Two studies were used to estimate the cognitive effort induced by task sequences and, hence, the effects that these sequences have on user performance. We found that sequences similar to the Object-Action task sequence induce less cognitive time than sequences similar to the Action-Object task sequence. A longitudinal study was then used to analyze user preferences for task sequences as novices became experienced users with using an interior design application. We found that novices and experienced users alike prefer sequences like the Object-Action over sequences like the Action-Object task sequence. / Master of Science