The task was to find the Landolt broken ring among the background circle. The Landolt was 20 × 20 pixels and it was designed according to ISO 8596. The size of the background circles was the same with Landolt ring. There was only one target in each trial and the gap may be at left or right. The display was a 47-inch LCD. The size of the screen was 1040mm × 590mm. Targets and background objects were green (R 0G 170B 80) and the background was white (R 255G 255B 255). The searching area can be divided into 64 × 40 boxes with the size of 20 × 20 pixels. The background objects and targets were arranged as shown in figure 1. At the beginning of the task, the target didn’t appear in 1st to 7th rows, 34th to 40th rows, 1st to 12th columns and 53th to 64th columns in order to avoid extremely long search time. In addition, to avoid too short search time, the target didn’t appear in 15th to 25th rows and the intersection area of the 11th to 29th rows and the 20th to 44th columns. The area that the target did not appear was shown in figure 2 (the dark area). In dynamic conditions, the target and background objects moved from left to right with a constant velocity. The area moving out of the right side of the screen would appear in the left side again. In each trial the velocity was randomly selected.