Amplitude adaptation occurs where a saccade is represented as a vector and not as its components

When saccades become inaccurate, their amplitude is adapted. We examined, in humans, whether this adaptation occurs where the saccade is represented as a vector or as its horizontal and vertical components. In one experiment, we behaviorally reduced the amplitude of clockwise oblique saccades and examined the transfer to saccades made to other target amplitudes and directions. In a second, we adapted rightward saccades of the same size as the rightward component of the clockwise oblique saccades and examined the effect on oblique saccades. The results of both experiments imply that adaptation occurs where the saccade command is represented as a vector.