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Background: Fatigue due to sleep restriction places individuals at elevated risk for accidents, degraded health, and impaired physical and mental performance. Early detection of fatigue-related performance decrements is an important component of injury prevention and can help to ensure optimal performance and mission readiness. This study used a predictive visual tracking task and a computer-based measure of attention to characterize fatigue-related attention decrements in healthy Army personnel during acute sleep deprivation. Methods: Serving as subjects in this laboratory-based study were 87 male and female service members between the ages of 18 and 50 with no history of brain injury with loss of consciousness, substance abuse, or significant psychiatric or neurologic diagnoses. Subjects underwent 26 h of sleep deprivation, during which eye movement measures from a continuous circular visual tracking task and attention measures (reaction time, accuracy) from the Attention Network Test (ANT) were collected at baseline, 20 h awake, and between 24 to 26 h awake. Results: Increases in the variability of gaze positional errors (46-47%), as well as reaction time-based ANT measures (9-65%), were observed across 26 h of sleep deprivation. Accuracy of ANT responses declined across this same period (11 %). Discussion: Performance measures of predictive visual tracking accurately reflect impaired attention due to acute sleep deprivation and provide a promising approach for assessing readiness in personnel serving in diverse occupational areas, including flight and ground support crews. [ABSTRACT FROM AUTHOR]

Background: Microgravity does not affect visual function directly. However, because of the altered afferentation from vestibular, support, and tactile-proprioceptive systems, it could lead to disturbances in visual tracking and inhibit the cosmonaut's activity. Therefore, it is neces-sary to obtain quantitative evaluations of spaceflight effects upon gaze control and vestibular-cervical-ocular responses. Methods: Examination of visual tracking with the head in a fixed position was performed in 26 Russian ISS cosmonauts before and after a prolonged spaceflight (129-215 d). As vestibular tests, we used several roll-tilts and yaw head rotations. Eye movements were recorded using both video-oculographic and electro-oculographic methods. Results: It was shown that until 9 d after landing (R + 9) spontaneous eye movements were increased (spon-taneous nystagmus, gaze nystagmus, square wave jerks); otolith function was suppressed (inversion, absence, or significant decrease of the com-pensatory torsional ocular counter-rolling); vestibular reactivity was elevated (an increased intensity of the vestibular nystagmus during head yaw rotations); amplitude and velocity characteristics of gaze control (saccades, smooth pursuit, gaze holding) were significantly decreased; total reaction time was significantly increased up to 2-3 times; and gaze holding ability was degraded. For several cosmonauts, smooth pursuit was collapsed and their gaze approached the stimulus or pursued its motion utilizing a sequence of saccades at least until R+5. Discussion: Prolonged exposure to microgravity considerably affects all forms of visual tracking. Revealed disturbances in precision of visual tracking and adoption of the new tracking strategy substantially prolong (up to 2-3 times) the period required to acquire, recognize, and to fixate gaze on the target. [ABSTRACT FROM AUTHOR]