A fixation task in which the subject will require to look at a target-a green circle (diameter ~1) sequentially presented at eccentric (15 rightward and leftward, 8 upward and downward) positions, each eccentric position being sustained for 20 s. Gaze-holding score will be assessed for each circle by approximating the gaze position coordinates by the least squares method to obtain the best correspondence using the fit function. The areas of the obtained ellipses, reflecting the spread of gaze position coordinates, will be determined for each of the four circle positions in each subject. Areas will be expressed in square visual degrees (sq. deg.)

Ten black circles (diameter ~1) will be presented on the monitor distributed pseudorandomly over the screen. Subjects will be instructed to count silently the number of points and give a verbal response. Study parameters: the performance time, the number of fixations, their durations, the total length of the scanning trajectory, and the saccade amplitude.

The subject will be required to follow a target jumping their gaze from one corner of the square to the next as quickly as possible as soon as a circle appeared; saccades will be required in order to do this (An image of a square with side length 10° will be presented on the monitor and a red circle (diameter ~1°) appeared in the corners sequentially in the clockwise direction.) Study parameters: the total number of saccades completed, the proportions of relatively accurate (A in the range 8.5-11.5°), hypometric (short, A < 8.5°), and hypermetric (long, A > 11.5°), and corrective saccades (occurring only after dysmetric saccades, 1.5° < A < 5°);

A clinical scale that is based on a semi-quantitative assessment of cerebellar ataxia on an impairment level.