Two patients suffering from primary cerebellar degenerative diseases and a healthy control subject undertook a walkway task demanding precise foot placement at each step. Vertical and horizontal eye positions were measured, using a head-mounted optics eye tracking system, and footfall was recorded throughout the task. The healthy subject stepped accurately onto all targets and produced a clear pattern of saccadic eye movements, fixating each target in the sequence just prior to footlift. A real-time video recording and still frame photographs, showing direction of gaze while walking, provide direct visual confirmation that these saccadic eye movements serve to transfer gaze between successive targets in the walkway sequence. This supports the proposal that the planning and subsequent generation of a saccade provides the locomotor control system with information useful for the feedforward planning of the corresponding leg swing. During the task cerebellar patients showed characteristic locomotor and oculomotor deficits (Crowdy et al. 2000). Dysmetric saccades to fixate the footfall targets were seen in 65 % of steps. Analysis confirms that these multi-saccadic eye movements were comprised of an initial hypometric saccade, which undershoots the target, followed by one or more smaller, additional saccades. Direct visualisation of gaze at the end of a saccadic sequence confirms that these additional saccades are indeed corrective, resulting in a foveal image of the footfall target. This study was carried out with local ethical committee approval and informed consent of patients and control subjects.

Crowdy, K.A., Hollands, M.A., Ferguson, I.T. & Marple-Horvat, D.E. (2000). Exp. Brain Res. 135, 437-454. these additional saccades are indeed corrective, resulting in a foveal image of the footfall target. This study was carried out with local ethical committee approval and informed consent of patients and control subjects.

Crowdy, K.A., Hollands, M.A., Ferguson, I.T. & Marple-Horvat, D.E. (2000). Exp. Brain Res. 135, 437-454.