OPEN-LOOP AND CLOSED-LOOP SMOOTH-PURSUIT EYE-MOVEMENTS IN NORMAL-CHILDREN - AN ANALYSIS OF A STEP-RAMP TASK

We previously reported that the visual ability to track a moving targe t (smooth-pursuit tracking) improves as children age from 8 to 15 year s old. This study used infrared oculography during step-ramp tasks to determine whether the age-related improvement in smooth-pursuit tracki ng is due to developmental changes in the ability to perceive and matc h eye velocity to target velocity (open-loop tracking). Infrared oculo graphy was used to assess the ability to track a moving stimulus (smoo th-pursuit tracking) during step-ramp tasks in 51 normal children betw een 8 and 15 years old. The first 100 msec of tracking (initial pursui t) occurs before any visual feedback (open-loop tracking) and represen ts sensorimotor transformation. Ongoing pursuit (measured by smooth-pu rsuit gain) includes feedback information as to the success of pursuit (closed-loop pursuit) and depends on sensorimotor transformation as w ell as higher order abilities, including the ability to sustain focuse d attention. Open-loop pursuit is not affected by age of the subject. In contrast, during closed-loop pursuit, when target step and target m otion are in opposite directions, age is significantly correlated with closed-loop pursuit gain, Spearman's R = 0.40, p < .003. The ability to perceive and match eye velocity to target velocity is fully develop ed by 8 years of age.