Smooth pursuit eye movements under open-loop and closed-loop conditions.

We measured smooth pursuit eye movement responses to sinusoidal target motion in the open-loop condition (target motion stabilized on the retina) and the closed-loop condition (target motion fixed in space). We also predicted the closed-loop response for each subject from the open-loop data, using the relationship for a linear system. Predictions made in this way were very accurate, for both gain and phase lag, even though responses of a given subject usually differed idiosyncratically from those of another. The accuracy of prediction was observed over a broad frequency range (0.5-3Hz) and a moderate range of target amplitudes (2-6 deg, peak-to-peak).