Table of cross-validated model errors, comparing the voxel model and the regionally homogeneous model. In each case the training error is in parentheses. Voxel MSE_rel refers to relative error, Equation 4, at the voxel level. This measure approximates the data normalized MSE for small errors, but is bounded to maximum of MSE_rel = 200%, which is achieved if either Y^true or Y^pred is 0 and the other is not (see Methods). Region MSE_rel is the error found after regionalizing the voxel model prediction. PTP (“power to predict”) computes MSE_rel for only those held-out experiments where there was another injection in that region which was not used for fitting.