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.

Lastly we pose the question as to whether express saccades can be obtained when the fixation spot and targets typically used in these experiments are presented not on a homogeneous background, but are superimposed on a complex visual scene. The complex visual scenes we used were still photographs of natural scenes or line drawings. They were presented on the monitor. Figure 42, top left, shows an example of one of the displays used. The three panels on the right show data collected concurrently with either a homogeneous background, with a steady patterned background and with the background appearing at the same time as the target. With the homogeneous background the now familiar bimodal distribution is obtained. With the steady patterned background there is no bimodal distribution but many saccades fall into the express range. When the patterned background came on with the target the monkey made no express saccades. These findings are in concert with those described in association with Figures 32 and 41.