Effect of saccadic amplitude adaptation on subsequent adaptation of saccades in different directions.

We have shown previously that adaptation of horizontal saccades exerts facilitating effects on subsequent adaptation of saccades in the same direction. Now we investigated the effect on saccades in different directions. A series of three alternating gain changes was induced by intrasaccadic step (ISS) of the target in two monkeys. The gain of saccades to horizontal or vertical target steps was decreased by backward ISS (conditioning). Then, we used forward ISS to increase their gain back to approximately 1.0. Finally, we induced a gain decrease for saccades to oblique target steps with backward ISS. We analyzed dependency of test adaptation rates on the direction of conditioning saccades. The rate of adaptation of the horizontal component of oblique saccades was significantly larger when conditioned with horizontal saccade adaptation than with vertical saccade adaptation. The rate for the vertical component did not show such differences. Following horizontal saccade adaptation, the horizontal component adapted faster than the vertical component. After vertical saccade adaptation, the vertical component tended to adapt at higher rates. Taken together, the results indicate that horizontal saccade adaptation exerts a facilitating effect on subsequent adaptation of the horizontal component of oblique saccades.