Figure 1.

Examples of visually guided saccades from healthy individuals and patients with progressive supranuclear palsy (PSP). In the first row of subplots (A,D,G,J), eye position is plotted on the y‐axis, and the x‐axis depicts the corresponding time in seconds. Black lines indicate the vertical eye position; green traces illustrate the horizontal eye position, gray dashed lines depict the baseline straight‐ahead position, blue dashed lines depict the position of the target (desired eye position), and arrows indicate interruption in ongoing saccades (the blue arrow illustrates 1 type of interruption in which the eyes continue to move at slower velocity during interruption, the green arrow depicts slower eye movement in the opposite direction, and the red arrows illustrate the cessation of eye movement during interruption). A illustrates a normal, visually guided vertical saccade from a healthy individual; D and G depict 2 examples of visually guided vertical saccades from the same individual with PSP; and J depicts eye positions during horizontal saccade. The middle row of subplots (B,E,H,K) depicts eye velocity: B illustrates the eye velocity of a normal, visually guided saccade recorded from the healthy individuals, and E and H depict vertical eye velocity during vertical saccades in PSP. The green line in K illustrates normal horizontal eye velocity during a horizontal saccade in PSP. In these subplots, eye velocity is plotted on the y‐axis, and the x‐axis illustrates the corresponding time. Red arrows indicate an interruption in saccade when the eye velocity was zero, the green arrow indicates when eye moved at slower velocity in the opposite direction, and the blue arrow indicates when eyes moved in the same direction at slower velocity. The bottom row of subplots (C,F,I,L) depicts trajectories of horizontal and vertical saccades: C illustrates a normal saccade from the healthy individual, F and I depict vertical saccade in PSP, and L is a horizontal saccade in PSP. Green dots indicate the start point, red dots indicate the stop point, and gray dashed lines are the desired path of an eye movement. Vertical saccades have a curved and serpentine path, depicting the clinical phenomenon of “round the houses” sign. Similar curvature is present in horizontal saccades as well, but it is much less robust.