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Shun-nan Yang; Curvature of Saccade Trajectory: The Dynamic Interaction of Anticipation-based and Stimulus-based Movement-related Activation. Journal of Vision 2003;3(9):432. doi: 10.1167/3.9.432.
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The curvature of saccadic eye movements is often observed when a certain region of the movement field is deactivated due to inhibition. Different explanations of this phenomenon have been offered. One of such explanations emphasizes the dynamic movement of activated areas during the process of saccade execution (the moving-hill hypothesis) and that the deactivation of a certain region forces the dynamic encoding of eye position to be altered in relation to the deactivated area.
This explanation predicts that when there is more than one source of saccade-related signal encoded in the movement field, the existence of one source may interact with the execution of a saccade controlled by another source. This should result in the dynamic change of saccade trajectory as determined by the relation of these two sources.
The current study investigates the predicted dynamic change of saccade trajectory by asking subjects to fixate at a visual target that changes its position periodically in a horizontal direction. Occasionally the new position of the target will deviate from the anticipated horizontal position vertically. The latency, landing position, and trajectory curvature of saccades were measured.
The results show that the trajectory of critical saccades following target deviation can be divided into three categories: When the latency of saccades is short, the eye is first sent to the anticipated location and then the deviated location; when the latency is long, the eye is sent to the deviated location directly; an intermediate latency leads to curved saccades, with the direction and degree of curvature being predicted by the relative position of the anticipated and the deviated location. These results support the moving-hill hypothesis, showing that the modification of activated movement field may be directly related to saccade execution. Further directions of research on saccade encoding and execution are discussed.
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