Smooth-pursuit eye movements are analyzed using a system analysis approach. Frequency domain methods are used to factor the smooth-pursuit response into a linear component and a nonlinear or remnant component. The linear component is that part of the tracking response that is linearly related to the target movement; the remnant is the component remaining after the linear component is subtracted out. Tracking abnormalities that are not evident by inspection of the complete eye-movement record become obvious upon inspection of the remnant.
