Fig. 7.

Graphical illustration of the proposed mechanisms that drive adaptation in patient RK. In the model it is assumed that RK's oculomotor system is impaired in processing mismatches between predicted and actual saccade landing errors for postsaccadic targets appearing in the left visual hemifield. A: a rightward saccade will typically undershoot the initial target at position T1. When the target is displaced inward to position T2, it will be seen in the left hemifield after the saccade has been executed. If the lesion in the VL nucleus disturbs error prediction, only the retinal error between postsaccade landing and the physical position T2 can be used for adaptation. Since the undershoot already brought the saccade closer to position T2, the retinal error is smaller than the mismatch derived from error prediction. Adaptation magnitude therefore should be decreased compared with healthy subjects. B: following the same logic, for a leftward saccade to a target T1, which will then be displaced in the outward direction, the typical saccade undershoot will lead to an increase in adaptation magnitude if the oculomotor system cannot rely on the error prediction mechanism.