The Neural Control of Visually Guided Eye Movements
C. Cortical Mechanisms of Visually Guided Saccadic Eye Movements

To study saccades made to single targets appearing in the visual field, monkeys were trained to first fixate a spot on a monitor and to then made a saccade to a single target that appeared at one of several locations on a monitor as depicted on top of Figure 9. It had previously been discovered by Fischer and Boch, that the latency distribution obtained when saccadic eye movements are made repeatedly to such targets, is bimodal. They named the first mode express saccades and the second regular saccades.