Among other functions, the neurological and neurovestibular systems serve to support positional awareness and motor control. Because gravitational cues and visual references play a role in this support, it is not surprising that the spaceflight environment profoundly influences static and dynamic positional sense and subsequent motor function. Human adaptation to this unique environment is being investigated to understand how performance may be optimized in every flight phase. Proper neurovestibular function ensures spaceflight crew safety in the complex and unfamiliar visual and motion milieu of microgravity and because of reliance on mechanical display information, enhances ability to operate a vehicle safely. The neurovestibular system creates a consistent, conscious map of head and body orientation as well as an internal orientation reference that will correct for absent or erroneous visual and somatosensory systems. It primarily stabilizes the eyes (the visual system) by means of (1) the vestibular ocular reflex, which is related to maintaining a stable world during movement; and (2) the vestibular spinal reflex, which preserves body alignment and establishes an appropriate relationship between the head and body. The character of the vestibular and visual systems' interaction depends on a specific task or relevant operational requirement. For example, whereas a crewmember depends on the visual vestibular ocular reflex to track a stationary target while turning, that same individual suppresses the vestibular ocular reflex when tracking a headfixed target, such as a head-mounted display, while turning. A person's pursuit system (slow eye movement) is used to track and identify moving objects, and the saccade system (fast eye movement) is necessary to acquire objects in the peripheral visual field and scan instruments. Visually induced optokinetic nystagmus occurs when a person views a moving background. This adds to the optical data that generates a sense of speed over terrain. [ABSTRACT FROM AUTHOR]