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Abstract:
Smooth pursuit eye movements change the retinal image motion of objects in the visual field. To enable an observer to perceive
the motion of these objects veridically, the visual system has to compensate for the effects of the eye movements. The occurrence of
the Filehne-illusion (illusory motion of a stationary object during smooth pursuit) shows that this compensation is not always perfect.
The amplitude of the illusion appears to decrease with increasing presentation durations of the stationary object. In this study
we investigated whether presentation duration has the same effect when an observer views a vertically moving object during horizontal
pursuit. In this case, the pursuit eye movements cause the perceived motion path to be oblique instead of vertical; this error in
perceived motion direction should decrease with higher presentation durations. In Experiment 1, we found that the error in perceived
motion direction indeed decreased with increasing presentation duration, especially for higher pursuit velocities. The results
of Experiment 2 showed that the error in perceived motion direction did not depend on the moment during pursuit at which the
stimulus was presented, suggesting that the degree of compensation for eye movements is constant throughout pursuit. The results
suggest that longer presentation durations cause the eye movement signal that is used by the visual system to increase more than the
retinal signal.
