“…Abnormalities include (1) a failure of eye velocity to match target velocity during sustained visual tracking (ie low closed-loop gain) (eg Clementz and McDowell, 1994;Sweeney et al, 1999;Levy et al, 2000; see Levy et al, 1993 for a review), which is thought to reflect deficits in predictive components of the SPEM response (Thaker et al, , 1999; (2) an increase in catch-up saccades, which is secondary to low gain (Abel and Ziegler, 1988;Sweeney et al, 1994); (3) decreased acceleration during pursuit initiation (Clementz et al, 1995;Ross et al, 1996), which may reflect retinal motion processing and/or anticipatory learning deficits (Chen et al, 1999;Avila et al, 2002a); and (4) an increased frequency of leading saccadic eye movements (Avila et al, 2002b;Levy et al, 2000;Ross et al, 2000), which may reflect a loss of cortical inhibitory control over saccades during pursuit (Litman et al, 1994;Ross et al, 1998;Lencer et al, 1999a).…”