The Influence of Motor Training on Human Express Saccade

26 27 Express saccadic eye movements are saccades of extremely short-latency. In monkey, 28 express saccades have been shown to occur much more frequently when the monkey has been 29 trained to make saccades in a particular direction to targets that appear in predictable locations. 30 Such results suggest that express saccades occur in large number only under highly specific 31 conditions, leading to the view that vector-specific training and motor preparatory processes are 32 required to plan a saccade of a particular magnitude and direction. To evaluate this hypothesis 33 in humans, we trained subjects to make saccades quickly to particular locations, and then 34 examined whether the frequency of express saccades depended on training and the number of 35 possible target locations. Training significantly decreased saccade latency and increased 36 express saccade production to both trained and untrained locations. Increasing the number of 37 possible target locations (2 vs. 8 possible targets) led to only a modest increase of saccade 38 latency. For most subjects, the probability of express saccade occurrence was much higher 39 than that expected if vector-specific movement preparation were necessary for their production. 40 These results suggest that vector-specific motor preparation and vector-specific saccade 41 training are not necessary for express saccade production in humans and that increases in 42 express saccade production are due in part to a facilitation in fixation disengagement or else a 43 general enhancement in the ability of the saccadic system to respond to suddenly appearing 44 visual stimuli. 45