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 de signed to promote best possible accuracy based only on the visual info rmation present in a single trial. Saccadic errors to point targets we re 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 perceptua l localization. This level of performance was maintained for targets u p to 3 deg in diameter. Corrective saccades were infrequent and limite d almost exclusively to the point targets, We conclude that the saccad ic system has access to a precise representation of a central referenc e position within spatially-extended targets and that, when explicitly required to do so, the saccadic system is capable of demonstrating re markably accurate and precise performance.