Comparison of the time evolution of the star formation in the four square regions used in Fig. 8 (top row) to that of the bar half-length (bottom row), for Model1 and Model2 (left and right column, respectively). Peaks in R_bar correspond to the times of bar-spiral connection. The frequency of these bar length peaks coincides with the frequency of the starbursts seen in the top panel (see number of peaks N_peaks in each panel), which suggests their correlation with the periodic bar-spiral overlaps. Starbursts do not always happen at the same time at the two ends of the bar.