Internal attentional brain states are challenging to study because their fluctuations are not always event related and can dynamically ebb and flow at multiple timescales. Traditional blood oxygen level dependent (BOLD) functional magnetic resonance imaging (fMRI) enables observation of the average response evoked by stimuli and/or behavioral response. However, task engagement inevitably fluctuates on a single-trial basis throughout the run of an experiment. Even simple target-detection perceptual decisions involve a complex cascade of neural processes including stimulus detection, target recognition/rejection, motor planning, and behavioral response, all of which are associated with evoked responses that vary on a single-trial basis (Philiastides et al., 2007). Many of these processes are time locked to stimulus onset, but others are more closely locked to the behavioral response (Gerson et al., 2005).
