(Color online) The time evolution shows the wave breakup and formation of a pair of counter-clock rotating spirals on a circular defect at t = 80 (a), t = 86 (b), t = 100 (c), t = 120 (d), t = 140 (e), and t = 300 (f). Other parameters: R = 15 △ x and ω=0.93ω₀.