Fast-paced technology advancements have enabled us to create ecologically valid simulations of high risk, complex, and semantically rich environments in which human interaction and decision-making are the keys to increase system performance. These advances have improved our capabilities of exploring, quantifying, and measuring the underlying mechanisms that guide human behavior using sophisticated neuroergonomic devices; and in turn, improve human performance and reduce human errors. In this thesis, multimodal approaches consisted of a self-report analysis, eye-tracking analysis, and functional near-infrared spectroscopy analysis were used to investigate how veteran local & en-route air traffic controllers carry out their operational tasks. Furthermore, the correlations among the cognitive workload and physiological measures (i.e. eye movement characteristics and brain activities) were investigated. Combining the results of these experiments, we can observe that the multimodal approaches show promise on exploring the underlying mechanisms of workload and human interaction in a complex, high-risk, and semantically rich environment. This is because cognitive workload can be considered as a multidimensional construct and different devices or approaches might be more effective in sensing changes in either the task difficulty or complexity. The results can be used to find ways to better train the novices.