The face-sensitive N170 and VPP components manifest the same brain processes: the effect of reference electrode site.

OBJECTIVE (1) To investigate the hypothesis that the vertex positive potential (VPP) and the N170 ERP components reported in the face processing literature are two manifestations of the same brain processes whose relative amplitude in a given experiment is dependent on reference electrode; (2) to investigate whether differences in face/object results reported in studies looking at the VPP and N170 are attributable to the location of reference. METHODS EEG was recorded from 53 scalp electrodes referenced online to the left mastoid while subjects viewed face, car and word stimuli. Off-line, the data were systematically re-referenced to the common average, averaged mastoids, averaged earlobes, non-cephalic, and nose. The correlation of timing, amplitude, and effects was investigated across reference electrodes. RESULTS (1) The amplitude of the N170 and VPP components varies in a precisely inverse manner across reference; (2) the peaks of the N170 and VPP are temporally coincident for all reference electrodes, (3) both components can be accounted for by the same dipolar configuration, and (4) the components show identical functional properties. CONCLUSIONS The VPP and N170 are two 'faces' of the same brain generators. SIGNIFICANCE The differential N170/VPP effects observed in ERP studies can be accounted for by differences in reference methodology.