Smooth pursuit deficits in space flights of variable length.

The maintenance of stable vision is a primary function of the neurovestibular and sensory-motor systems. There is, however, strong evidence suggesting that space flight results in a modification of the central nervous system and subsequent control of ocular-motor responses. These changes effect those neural mechanisms which are responsible for holding images steady on the retina during brief, self-initiated, head rotations or during the voluntary pursuit of moving targets. Recent studies have shown significant saccadic intrusions in both of these experimental paradigms, including an inability to null the vestibulo-ocular reflex (VOR) during the head/eye pursuit task. The maintenance of vision, while not entirely stable, both inflight and immediately postflight is now believed to be due to neural strategies that evolve for the purpose of assisting in directing the moving target onto the retina.