Such complementary multimodal results can be simply merged by utilizing the cross-modal relationship, derived and discussed in Section III. That is, the BOLD effect size estimated from the fMRI signal in each voxel is proportional to the time integral of the local source power underlying the ERP/ERF signals. (4)∫Tss2(r,t)dt∝β(r) where s2 (r,t) is the source power at location r and time t, β(r) is the quantified BOLD effect size at location r. TS is the duration of the electrophysiological response induced by a transient stimulus or task, which is referred to as the “event-related period”.
