Selective and delayed adaptations of human saccades

Saccades are jump-like eye movements to a target, controlled in a feedforward manner so that they do not deviate in response to intrasaccadic target shifts. Instead, systematically induced intrasaccadic target step back gradually reduces the first saccade amplitude due to adaptation in order to catch the first target on the fovea by a single saccade. Inspired by the context-specific adaptation of the vestibule-ocular reflex, we investigated selective adaptation of three types of human saccades by using Deubel's modified version of the double step paradigm (1986, 1987). Saccades to a jumping target (visually-guided externally-triggered saccade, VE-saccade), a stationary visible target (visually-guided internally-initiated saccade, VI-saccade) and a remembered target (memory-guided saccade, M-saccade), which have different peak velocities and accuracies, showed unique adaptive capabilities, as shown by other authors with respect to the VE-saccade and VI-saccade in our paradigm. Even when the target step back was consistently delayed by up to 400 msec from the end of each first saccade, such adaptation still occurred. These results suggest that the adaptation of saccades should take place during or shortly after the first saccades and should be closely related in time with the perception of the first saccade errors.