Effect of mean reaction time on saccadic responses to two-step stimuli with horizontal and vertical components

Saccadic responses to target movements containing two horizontal, two vertical and paired horizontal-vertical steps were measured in three human subjects. In all three target conditions, subjects made predominantly one saccade for short interstep intervals (ISI) and two saccades for long ISIs. However, the percentage of two-saccade responses (% 2 saccades) at each ISI varied substantially among target conditions and subjects due to inter-experiment variability in mean single step reaction times ( RT). Correlation of % 2 saccades with the normalized interval RT minus ISI reduced interexperiment variability and suggested a sigmoid curve that applied to all our subjects and most other data taken from the literature.