Illustration of the phase bifurcation index with hypothetical data. The index is computed as Φ = (ITC₁ − ITC_all) × (ITC₂ − ITC_all), where ITC_1,2,all is the intertrial coherence in conditions 1 and 2 and in both conditions combined. Each line segment represents a trial, with its angle representing phase at the frequency and time point of interest. The left circles illustrate global phase distributions, while the right circles show the two experimental conditions separately. A, Both conditions are phase locked at opposite angles. As a result, the ITC of both conditions combined is close to zero, resulting in a strong positive Φ. This is equivalent to the hypothesis that hits and misses are each associated with different phase angles. B, The null hypothesis states that both conditions are randomly distributed, resulting in a Φ close to zero. C, Only one condition is phase locked, and the other is randomly distributed. The resulting ITC of both conditions is stronger than the ITC of condition 1, but smaller than the ITC of condition 2, resulting in a negative Φ. This situation is expected during the ERP time range, where an ERP is present only for detected stimuli. D, Both conditions are strongly phase locked at the same phase angle; the resulting Φ is close to zero.