Smooth pursuit eye movements in response to unpredictable target waveforms.

Humans track smoothly moving objects with a combination of saccadic and smooth pursuit eye movements, called dual mode tracking. A pseudo random ternary sequence was used to generate an unpredictable target motion that had linear ramps of random velocity and duration. This aperiodic waveform eliminated the subject's ability to predict target motion. Saccades were removed from these records leaving only smooth pursuit eye movements, called single mode tracking. Transfer functions were computed for both single and dual mode tracking. The difference in the transfer functions between 0.7 and 1.0 Hz is an indication of the quality of the smooth pursuit tracking which decreases with increasing target waveform bandwidth and with fatigue. The coherence function provides another quantitative measure of smooth pursuit tracking.