The GLM of the model-based analysis was extended with a second parametric regressor for absolute orientation energy (i.e., energy for the presented orientation) in a way that any variance shared between the energy and the CPE regressor would be accounted for by the energy regressor. (A) Whole-brain t-map for a positive relationship between BOLD signal and confidence prediction error (CPE), after accounting for absolute orientation energy (threshold: p < 0.001, uncorrected). Even after this correction for stimulus energy, a strong positive relationship in bilateral ventral striatum (left: peak at [−16 8 −10], t28 = 7.34, prFWE < 0.001; right: peak at [14 14 −6], t28 = 7.53, prFWE < 0.001) and in the ventral tegmental area (peak at [−6 −22 −16], t28 = 2.98, prFWE = 0.028) was present. (B) The converse model, in which variance was first accounted for by the CPE regressor and second by the energy regressor, showed no residual activation in the mesolimbic ROIs (even at a liberal threshold of p < 0.05, uncorrected). The strongest trends for a modulation by stimulus energy on top of CPEs was present in voxels located within our stimulus localizer ROI (left occipital cortex: peak at [−42 −74 −8], t28 = 2.85, p = 0.004, uncorrected; left posterior fusiform gyrus: peak at [−32 −56 −12], t28 = 2.60, p = 0.007, uncorrected). Interestingly, the modulation of activity in putative V1 by CPEs (cf. Supplementary file 2) appears to be entirely accounted for by CPEs, as no significant modulation by energy was detectable in this analysis (p > 0.05, uncorrected). (C) Whole-brain t-map for a positive relationship between BOLD signal and energy, without correcting for CPE. No cluster survived correction for multiple comparisons at the whole-brain level. The strongest activation was found in right dorsolateral prefrontal cortex (peak at [32, 38, 18], t28 = 5.24, p = 0.000007, uncorrected). A second notable activation was found in our stimulus localizer ROI (left fusiform gyrus: peak at [−32, −56, −12], t28 = 3.89, p = 0.0003, uncorrected).