The Neural Control of Visually Guided Eye Movements
D. Temporal Factors in Visually Guided Saccadic Eye Movements

3. Summary: basic facts and conclusions about express saccades.

• Express saccades occur only when single targets are presented.

• Extensive training is required for them to emerge.

• The generation of express saccades is greatly facilitated by introducing a gap time between the termination of the fixation spot and the appearance of the target.

• Express saccades do not occur when multiple targets appear necessitating target selection.

• Express saccades do not occur to targets appearing at unexpected locations.

• Express saccades do occur to targets that have newly shown color, shape and size as long as they appear at familiar, expected locations.

• What is learned for express saccade generation is the saccadic vector generated, not the absolute or relative position of the targets in space and not the orbital position of the eye.

• The probability with which express saccades are generated decreases with increasing sample size.

• Express saccades do occur when the pursuit and vergence systems are co-activated.

• Express saccades do occur when single targets appear at expected locations on a complex, patterned background.

• Express saccaces occur to the second of two successive targets whether this second target necessitates an eye movement away or toward the initial fixation spot.

• Pre-cuing the location of an impending target can increase the frequency of express saccade production when single targets are presented.

• Saccades after short-latency fixations that fall into the express range do occur under natural viewing conditions but no bimodal distribution of saccadic latencies is formed.

• Express saccades are eliminated by SC lesions, but not by V4, MT, V4+MT, magno, parvo, FEF and MEF lesions.