The Neural Control of Visually Guided Eye Movements
D. Temporal Factors in Visually Guided Saccadic Eye Movements
          1. The conditions under which express saccades can and cannot be generated.

d. Does the number of target locations used in a given sample at which a single target is presented affect the frequency with which express saccades are generated?

distribution of saccadic latencies with different numbers of target positionsFigure 33 shows the distribution of saccadic latencies when one, two or four target locations are used in the sample. On each trial a single target appears at one of these locations arranged in a randomized order. For each set the animal was run repeatedly for more than 400 trials. Exposure to each condition for 30-50 trials before data collection prepares the animal for the condition. The data show that there is a dramatic decrease in the number of express saccades made as the sample size of target positions increases. This monkey made few express saccades when four target locations were used. Thus the number of expected target positions used in any given sample is an important variable: the larger the sample, the fewer the number of express saccades.