Predictable Target Motion Research Articles

Frequency characteristics of the smooth pursuit component in tracking eye movements.

Frequency responses of the human eye tracking system vary remarkably according to the motion of the visual target. In general, periodic (predictable) target motion yields a higher gain and a smaller phase lag in comparison with random (unpredictable) target motion. This paper deals with the question of which of the saccadic and smooth pursuit systems causes this variability. Two kinds of target motions, sine (predictable) and Gaussian random (unpredictable) waves, were presented to the subject with either of two instructions: to fixate on the target or to fixate on the target and do mental arithmetic simultaneously. Recorded eye movements were separated into their saccadic and smooth components, and the respective frequency characteristics were analysed. The result shows that the large phase lag in non-predictive tracking is mainly due to the saccadic system. At low frequencies, the smooth component reveals a rather large phase lead in non-predictive tracking but not in predictive tracking. We also descri...

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.