Fig. 9.

Modifications to SC nonlinear gain field, tv, with acute lesions in the left SC map (only tv changes in the default parameter set). The control case uses a symmetric NL mapping (solid curve) as the combined effect of both colliculi with overlapping rostral zones; a range of ±20° gaze shifts is provided for rightward or leftward saccades (positive, via left SC; negative, via right SC to contralateral brain stem). A: a rostral lesion on the left colliculus shifts the minimum of the tv curve (dashed curve) toward the healthy side by ∼2° (the size of the rostral area; May 2006). B: a unilateral lesion on the left caudal colliculus in addition to displacement of the balance point (similar to A) reduces the slope of that arm of the tv curve. The severity of the displacement of the balance point and the slope change due to a caudal lesion depend on the site and severity of the lesion (compare the exemplary lesions illustrated with the dashed and dotted tv curves in B with their impact on position trajectories in Fig. 10E).