Figure 8.

Grand mean trial waveforms reflecting posterior medial frontal cortex (pMFC) and lateralized motor-related potentials, and their association with errors. A) Grand mean waveforms for the pMFC source cluster and left (SMC-L, projected to site CP3) and right (SMC-R, CP4) clusters putatively reflecting sensorimotor cortical sources are averaged within trial accuracy (dashed trace = correct; solid trace = error) and the correct-response hand mapping (blue trace = right hand; green trace = left hand). Horizontal bars denote regions of the waveform that were significantly associated with errors (blue = correct-response right hand; green = correct-response left hand), accounting for a stimulus congruency interaction term. For comparability, trials and subjects contributing to SMC-L and SMC-R waveforms were identical to that of the pMFC cluster (unmatched subjects were included based on Euclidean distance in clustering measure space, see Method section). B) Lateralized readiness potentials (LRPs, labeled with navy arrows) were revealed by summing the scalp projections for SMC-L and SMC-R clusters, and subtracting the ipsilateral from contralateral waveform, consistent with guidelines reviewed by Smulders and Miller (2011). Note that the polarity of the LRP peak (approximately −75 ms in response-locked waveforms) in (B) encodes the response hand mapping, such that it is negative-going for correct contralateral responses (dashed trace; LRP_COR) and positive-going for erroneous ipsilateral responses (solid trace; LRP_ERR).