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.

k. Are express saccades produced under natural viewing conditions?

To determine whether express saccades are generated in everyday life, we had monkeys view complex visual scenes presented on the monitor they faced and while they looked around in a room in which there were other monkeys as well as humans. Figure 41 shows the distribution of fixation durations while a monkey explored the scene with eye movements. Fixation durations of 105ms and less are common, which puts them into the range of express saccade generation for the ensuing saccade. However, the distribution appears to be unimodal. Thus it appears that saccadic latencies in the express range do arise in real life situations but that there is no evidence for a bimodal distribution.