Individualized EEG source reconstruction of Stroop interference with masked color words

A masked version of the classic color Stroop task was used to study interference effects with stimuli of variable visibility. Pattern masks with different stimulus onset asynchronies (SOAs) reduced the visibility in three steps. We took EEG recordings to measure neural correlates of Stroop interference and their relation to stimulus visibility. The analysis of event-related potentials indicated that N400 differences between congruent and incongruent trials varied with the degree of visibility, leaving no differences with stimuli near identification threshold. An equivalent current dipole model (ECD) was used to map source activity onto regions known to reflect interference-related activity. As expected, the anterior cingulate cortex (ACC) signaled the biggest differences between congruent and incongruent trials. As with event-related potentials, these differences disappeared with reduced stimulus visibility. In addition to equivalent current dipole modeling, Stroop-related neural sources were confirmed by means of current density reconstruction (SWARM) based on individualized boundary element models (BEMs) and a cortical constraint.