Time course of maximum cluster size for different clustering thresholds Time courses of phase-locked clusters obtained from the PLVz matrix. Red, green and blue lines represent the clustering result when the clustering threshold = 7.0, 8.0, and 9.0, respectively in PLVz units. The y-axis indicates the maximum cluster size at each time. Here, the cluster size is defined as the number of recording electrodes that belong to the identical cluster. Horizontal lines above each figure represent the periods during which the maximum cluster size is significantly larger than that in the self-paced key press condition.