Electrophysiological evidence for automatic processing of erroneous stimuli

• Automatic processing of erroneous stimuli was found in a task irrelevant dimension.
• Misspelled words evoked an effect in the 4–12 Hz band, 100 ms post presentation.
• Localization of this early effect showed strongest activation in the ACC.
• Behavioral Stroop interference of incongruent stimuli was reduced in misspelled stimuli.

In a paradigm combining color-word Stroop and misspelled words processing, spelling mistakes were placed in half the Stroop stimuli. Participants were presented with words written in different ink colors and asked to identify the color of the ink while ignoring the word meaning. Importantly, whether the word was correctly spelled or not was completely irrelevant to the task. The spelling manipulation did not change the phonology or semantic meaning of the words. Congruency and spelling correctness were manipulated orthogonally and interacted at the behavioral level. Event-related potentials showed a very early processing of misspelled words. The present findings are in line with the idea of anterior cingulate cortex (ACC) involvement in cognitive monitoring, expressed mainly in the theta frequency band. The present study demonstrates that this monitoring mechanism is elicited automatically, in other words, this mechanism perceives erroneous stimuli even when they are absolutely irrelevant to the participant׳s task. At later processing stages, the same central monitoring mechanism is also involved in the detection/resolution of conflict.