A comparison of oculomotor pursuit of a target in circular real, beta or sigma motion.

Pursuit of a point target in real or apparent motion upon a dark, diffusely lighted or structured background was recorded with a scleral coil technique. Smooth and saccadic components were separated and analyzed with computer techniques. Sigma-pursuit was superior to pursuit of beta- or real motion: smooth pursuit gain was higher, saccadic rate was lower and the detrimental effect of a structured background was smaller. Due to directional errors, smooth pursuit velocity often exceeded target velocity when this was smaller than about 10 degrees/sec. However, the smooth component in the correct direction of the target motion had a gain less than or equal to 1.0 and decreasing at higher target velocities for all pursuit modes, inclusive sigma-pursuit.