The accuracy and precision of saccades to small and large targets

Subjects made saccades to point and spatially-extended targets located at a randomly-selected eccentricity (3.8-4.2 deg) under conditions designed to promote best possible accuracy based only on the visual information present in a single trial. Saccadic errors to point targets were small. The average difference between mean saccade size and target eccentricity was about 1% of eccentricity. Precision was excellent (SD = 5-6% of eccentricity), rivaling the precision of relative perceptual localization. This level of performance was maintained for targets up to 3 deg in diameter. Corrective saccades were infrequent and limited almost exclusively to the point targets. We conclude that the saccadic system has access to a precise representation of a central reference position within spatially-extended targets and that, when explicitly required to do so, the saccadic system is capable of demonstrating remarkably accurate and precise performance.