Express saccades: the effects of spatial and temporal uncertainty.

Once trained to make express saccades, monkeys continue to make express saccades when there is a high level of uncertainty about both the location and the time of onset of a peripheral target. Providing additional information about the location and the time of onset of a peripheral target does not increase the frequency of occurrence of short latency saccades. Furthermore, the metrics of saccades with express latencies are typical of visually-guided saccades, rather than anticipatory movements or saccades to the remembered location of a target. Finally, practice on the gap paradigm restricted to one target location always viewed from the same initial eye position does not increase the probability of producing express saccades to the same target from other initial eye positions. Instead, the practice effect is specific to targets that have the same relative location, regardless of initial eye position.