An adaptive EEG derivation technique

The amount of common components in EEG tracings relating to any two electrodes in the 10-20 array depends partly on the distance between these electrodes, i.e. potentials on the scalp surface have an average mutual coupling which is related to distance along the surface. This coupling is expressed by the spatial correlation function which can be computed from the tracings. Information contained in the correlation functions relating to 30 individual subjects was used to modify the derivation technique to yield 'focussed' tracings in each case, i.e., tracings from which the distance-related coupling ('blur') had been removed. Obtained results were considered representative of the topographical resolution achievable within the limitations of the 10-20 system of electrode placement. The tracings were in most cases found to be almost identical to those obtained by means of the non-adaptive deconvolving technique known as source derivation. In some cases the adaptive technique produced tracings with slightly higher topographical differentiation than did source derivation.