Abstract: The human anterior cingulate cortex (ACC), which is active during many conflict-monitoring tasks, is believed to participate with the prefrontal cortex in a distributed network for conscious self-regulation. The hypothesis of this study predicts that conflict-related ACC activation will occur only when the conflicting stimuli are consciously perceived. Consistent with this view, Dehaene found that subliminal conflicts are resolved without ACC contribution under the subliminal conflict paradigm. Other studies have also found that the awareness of conflict is a precondition for conflict adaptation. However, other researchers have challenged this tight relation between awareness of conflict and conflict control. To clarify the relation between the awareness of conflict and conflict adaptation, we investigate conflict in the absence of consciousness by relying on the SNARC effect. Participants are probably not explicitly aware of conflict on the parity judgment task. In our study, the SNARC compatible trial is a congruent trial and the SNARC incompatible trial is an incongruent one. For the purposes of analysis, we divide the incongruent trials into two categories: those that follow compatible trials (labeled here as cI), and those that follow incompatible ones (labeled here as iI).
High-density event-related potentials (ERPs) were recorded to examine the electrophysiological correlates of conflict adaptation. The stimuli consisted of the digits 1, 2, 3, 4, 6, 7, 8, and 9. Each trial began with the presentation of an Arabic number; the number was presented for 300 ms at the center of the screen, after which it disappeared. After a varied interval of 1200–1800 ms, the next trial began. The study consisted of 640 trials, with the number of iI and cI trials being the same. The experiment consisted of two separate sessions in which the mapping of parity to the response side was varied.
The results indicated that the interaction between magnitude and side of response was significant, suggesting a clear SNARC effect on RTs. The RTs for the cI trials were significantly slower than those for the iI trials, indicating a clear conflict adaptation effect. For stimulus-locked waveforms, the N2 showed peak differences—between the cI and iI conditions—to be maximal at Fcz in the 260–300 ms interval after the target. No significant difference emerged between congruent and incongruent trials. A voltage map of the difference wave showed strong activity at the frontocentral region. The dipole analysis (BESA software) localized the generator of the difference wave (cI minus iI) in the dorsal ACC.
The study found the conflict adaptation effect in the SNARC effect, which is inconsistent with the classic conscious monitoring view. Since there may be some debate on defining the parity judgment task as a conflict task, we are aware that caution needs to be exerted in drawing firm conclusions from our study, which adds to the ongoing debate of the role of the ACC in cognition

Key words: conflict monitoring, SNARC effect, conflict adaptation, anterior cingulate cortex, event-related potentials