Do performance-monitoring related cortical potentials mediate fluency and difficulty effects on decision confidence?

It remains unclear to what extent the performance-monitoring (PM) processes involved in perceptual decisions are also involved in more complex reasoning decisions. To address this problem, we examined whether PM-related cortical potentials known to correlate with confidence ratings in the context of simple perceptual decisions also correlate with confidence ratings in a more complex reasoning task. In an EEG experiment, 49 participants had to quickly decide whether an equation (e.g. 9 * 7 = 65) was correct or incorrect and then report their confidence in that decision. Task difficulty and response fluency were varied to manipulate confidence. Pooling responses across correct as well as incorrect trials, we analyzed amplitudes of Error-Related Negativity (pooled ERN) and Error Positivity (pooled Pe). We found that pooled ERN but not pooled Pe had a positive significant correlation with decision confidence and that unpooled ERN correlated with confidence for correct, but not for error trials. Further analysis indicated that although pooled ERN correlated with task difficulty, neither pooled or unpooled potentials mediated the effects of difficulty or fluency on confidence. These results suggest that pooled ERN might reflect implicit performance monitoring and that confidence for simple perceptual and complex reasoning decisions may rely on different neural mechanisms.