We are not proposing a discrete anatomical structure that we purport to be the “Internal Monitor,” but, consistent with the top-down, engineering-based approach, the disparate signals and functions proposed for the IM are grouped in one block for clarity. Interestingly, recent work has uncovered the presence of many of these signals in the paramedian tract (PMT) (Nakamagoe, Iwamoto, & Yoshida, 2000 ) and, at the cellular level, climbing fiber activity has been shown to predict interval times allowing neurons to work as timers, such as those used in the IM to make logical decisions regarding visually guided, corrective, and braking saccades (Durstewitz, 2003 ). Similarly, we do not speculate on possible anatomical sites for each functional block (e.g., fixation and the superior colliculus) or discuss the putative roles of specific neurons (e.g., omnipause and burst cells) known to play a part in ocular motor control. In fact, we do not even claim that the specific functions identified separately in the model are necessarily anatomically distinct. Individual functional blocks aid in our understanding their respective roles in ocular motor control. Therefore, we made no effort to streamline the model by combining functions; we remain mindful of how prior attempts to use the final common NI to perform too many tasks limited those models’ capabilities and rendered them unable to simulate dysfunction (see below) (Abel et al., 1978 ). Although we named blocks for their functions in this model, we believe each is present in the normal OMS (e.g., the Braking/Foveating Saccade Logic block is probably the same mechanism used to program fast phases of vestibular and optokinetic nystagmus; the common stimuli for all are eye motion and retinal slip). Data supporting the common origin of fast phases and braking saccades appear in Figure 6C . Shown are vestibular fast phases in the response of a subject with a low-gain VOR secondary to multiple sclerosis. These braking saccades (up to two per VOR cycle) were generated despite the hi-frequency head oscillation. This suggests an innate ability for the ocular motor system to generate braking saccades in response to vestibular input. Thus, their common appearance in CN waveforms does not represent a newly developed, adaptive skill but rather, an exaptation (i.e., performance of a new function) (Gould, 1991 ) of the normal fast-phase mechanism. Until such time as neurophysiologists sort out all of the relevant anatomical sites, we prefer to err on the side of redundancy and separation of function, a more instructive and physiological approach.