My work aims to understand how internal goals and external environments influence voluntary task selection. The primary goal of my research is to understand the mechanisms underlying cognitive flexibility, the ability to switch between tasks or behaviors quickly and efficiently. Cognitive flexibility is disrupted in several mental health disorders such as psychosis, addiction, and autism. Most studies of cognitive flexibility rely on external cues to determine when and which task to perform, but in the real world this choice is under our voluntary control. While external influences may make these decisions difficult, e.g., seeing ads for junk food when we are trying to make healthy choices, they are nevertheless under a degree of internal control. My work takes the unique perspective of focusing on voluntary control in cognitive flexibility. I take a multimodal approach, using brain imaging (fMRI) and measures of electrical brain activity (EEG) to examine the dynamics of the underlying neural mechanisms, and electrical brain stimulation to better understand brain-behavior causal links. More recently, I've been applying computational modeling to determine the exact components underlying task selection. The long-term objective of my research is to understand the factors that limit flexibility to better inform treatments for psychopathology and to maximize flexibility in healthy individuals.