Fig. 2. Experimental set-up used to study the head movements during the `walking condition'. The black line drawn along the sagittal axis of the head allows angles corresponding to each nystagmic beats of the OCR to be measured. The corresponding duration is given by the time code. (A) Onset of a slow phase triggered by an anticlockwise stimulation; (B) end of the slow phase. Ob, optokinetic ball; Sc, screen; Tm, treadmill.