Express saccades are the fastest eye movements humans are able to make in response to something new.
We investigated temporal and spatial influences of distractors on express saccades. We know that target-driven saccades are affected differently by the presence of close and remote distractors. Distractors close to the target affect the saccade landing position (known as the "global effect"), while remote distractors prolong saccade latencies to the target (known as the "remote distractor effect"). Little is known, however, about whether a population of saccades known as express saccades (saccades with very short latencies between 80 and 130 ms) is similarly affected by close and remote distractors, as these saccades are considered to be the result of advanced preparation of an oculomotor program towards the target.
Using a gap-paradigm, cues, warning signals and feedback, we designed a task in which we were able to generate a large number of express saccades. The resulting saccade latency distribution displayed a separate and very early peak of express saccades; a distribution that was different from that of regular saccades. Our results also show that irrelevant and unexpected visual input had a large effect on express saccades. We found both a global effect and a remote distractor effect similar to those seen in regular saccades.
Even though our findings confirm the existence of very short latency saccades in humans, it is questionable whether they represent a different population of saccades as they were equally affected by the presence of distractors as regular saccades. On the basis of these findings we conclude that express saccades are very fast regular saccades.
Heeman J., Van der Stigchel, S. & Theeuwes, J. (in press). The influence of distractors on express saccades. Journal of Vision. [pdf]