Let us assume that a certain process or function (i.e., condition, group, or interaction thereof) is represented by neuronal generator activity that may be conceptually summarized by a single dipole, and that a second process is represented by a different neuronal activation resulting in a dipole of the same strength but with a different orientation (Fig. 14A). If the surface potentials stemming from either dipole are recorded from two scalp sites, one serving as the reference for the other, placed in line with the orientation of one the two dipoles, a greater potential will be measured for the in-line dipole (green) compared to the out-of-line dipole (red). This will lead to the conclusion that the first process (green) yielded a larger EEG signal than the second process (red). In contrast, if the surface potentials stemming from the same two dipoles are measured from two scalp sites placed at a right angle to the orientation of the green dipole (Fig. 14B), a greater potential will be measured for the red dipole. Hence, this reference scheme will lead to the opposite conclusion
