measures. Additional challenges may be further appreciated by considering the highly different temporal scales of the hemodynamic and electrophysiological responses. Table 1 lists typical values related to the temporal and frequency features of the single-trial ERP/ERF and BOLD signals. A quantitative cross-modal relationship is even more obscured when the electrophysiological signal is analyzed in an event-related manner while the hemodynamic signal changes across prolonged periods as in block-design experiments.
