ABSTRACT
Numerous forms of motor activity are carried out by humans in the course of their daily existence; of these, eye movements are generated with perhaps the least conscious awareness. Nonetheless, proper execution of the various forms of ocular motor behavior is essential for the successful acquisition of information about the environment. Because deficits in eye movement control can interfere with this information acquisition, performance on everyday tasks and neuropsychological tests alike may be impaired. A drug that markedly increased saccadic latency would interfere with any task requiring rapid refixations; a similar effect would be seen if saccadic accuracy were markedly reduced. An increase in duration, on the other hand, would be unlikely to have significant functional implications, since the time needed to execute a fast eye movement is much less than that needed to initiate one. Smooth-pursuit defects would generally be expected to be less significant functionally, since reduced pursuit gain elicits compensatory “catch-up” saccades in response to the resultant position error. Nonetheless, tasks requiring continuous fixation of a smoothly moving target would be more poorly executed following administration of a drug that markedly reduced gain. Because of the close relationship between smooth pursuit and suppression of the vestibulo-ocular reflex, performance on tasks requiring a subjects' fixation on a target moving with him would most likely be impaired, as well. In general, it is important to note that tests designed to evaluate various aspects of information processing could suggest high-level functional impairment when, in fact, the poor performance observed was due to drug-related abnormalities in ocular motor activity needed for initial information acquisition.
