The ability of the saccadic system to change motor plans in scanning letter strings.

Evidence from recent studies bolsters the idea of preestablished motor plans in scanning isolated items. Thus, refixation saccades are preplanned at the same time as the primary saccade directed to a peripheral item and are completed with fixed amplitudes irrespective of the first fixation position in the item. In order to examine the saccadic system's ability to correct the motor plan during its execution on the basis of new visual information, an experiment was conducted in which 11-letter strings were changed to two 5-letter strings at different times after the primary saccade was directed to the stimulus. The results demonstrate that the saccadic system is able to cancel the preplanned refixation saccade and plan a saccade directed to the next item only when the new visual information is available at least 220 msec before the execution of the saccade.