The Neural Control of Visually Guided Eye Movements
D. Temporal Factors in Visually Guided Saccadic Eye Movements
          1. The conditions under which express saccades can and cannot be generated.

h. Is the production of express saccades contingent on the position of the targets in space, on the orbital position of the eye or on the saccadic vector generated?

Two experiments were conducted to answer this questions. In the first, targets were placed at set locations on the monitor and the fixation spot was moved to selected sites enabling us to determine whether express saccades generation depends on the position of the target in space or on the vector of the saccades produced. This animal, as shown in Figure 37A, made few express saccades to a target at 45/3 that required a 45/3 saccadic vector. By contrast, as shown in Figure 37B, many express saccades were made to a target at 225/3 that required a vector of 225/3. This was the animal's natural disposition. When the fixation spot was moved to 45/6 and the target to 45/9, which generated the same saccadic vector of 45/3 as in Figure 37A, few express saccades were made; this is shown in Figure 37C. On the other hand, as shown in Figure 37D, many express saccades were generated to the target at 45/3 that necessitated a saccadic vector of 225/3. The target in Figure 37D is in the same position as in Figure 37A. The findings suggest that the crucial factor in express saccade generation is the saccadic vector, not the position of the target in space.