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Future helmet mounted systems and cockpit displays will rely on color graphics and information that high performance aircraft pilots will need to discern and understand. Color in displays may help reduce pilot workload. The effect of high G and reduced eye level blood pressure on field-of-view has been study extensively. The effect of high sustained acceleration on color vision, however, is unknown. Research on visual contrast sensitivity, night vision, and visual acuity under acceleration in a human centrifuge has demonstrated changes in vision. We began by having normal color vision subjects view a magnified color aerial map and describe what they saw as we slowly ramped up the G profile from baseline (1.4 G) at 0.1G/sec until they experienced almost complete blackout. At that point subjects began straining and the centrifuge was rapidly decelerated. Several subjects described the river fading away before much else happened. Then the yellow and green features of the terrain faded together. Reds and dark blues appeared to change to black but remained legible until the entire image also faded to black. Computer types call the color of a river on a map cyan. So a display was created that resembled a device know as a "light bar" that is routinely used in centrifuge research. It consisted of a 45 degree wide square projection of green dots in the periphery and a red dot in the center on a white background. Due to our new curiosity about cyan we added dots halfway between the green and red that were cyan. We then ran several people through the same slow onset ramp until near blackout. Several reported that the cyan disappeared completely, significantly before the green. Then the green disappeared, and finally the central red dot. For those who experience it, it is a very useful and repeatable early end point where vision is affected but still available. Next we borrowed a color wheel from the hypobaric chamber and taped it to the wall of the cab. Several subjects reported discomforting angular optical vection due to torsional nystagmus. Thus, a vertical bar arrangement of colors was selected that minimized disruption from involuntary eye movements.

Objective: To generate, on a multi-axial centrifuge, a negative to positive acceleration profile that reproduces the physiological reaction and subjective symptoms experienced by agile aircraft pilots. Previous research will be summarized and current status of research described., Methods: Experiments have been accomplished with the Dynamic Environment Simulator (DES) using different profile generating techniques. The DES was programmed with a set of open-loop profiles that provided five second duration baseline exposures ranging from +1.4 Gz down to -2 Gz followed by rapid transition to positive G levels up 2 to 8 +Gz. Volunteer subjects were instrumented and trained to report visual symptoms., Results: Both profile generation approaches produce the reduced cardiovascular and subjective tolerance in a subset of subjects tested. Accumulated stress and motion sickness are factors in quantitative measures. Use of the anti-G straining maneuver may only temporarily alleviate the symptoms with a second period of visual symptoms even as the G load is removed. Positive pressure breathing for G (PBG) does not appear to exacerbate the effect, but the advantages gained from PBG may be lost when a sustained G pull is preceded by a negative G push., Conclusions: The utility and limitations of using a multi-axial centrifuge for the study of negative to positive G transitions have been described. Greater study is necessary on multiple factors affecting the effect and large numbers of volunteer subjects are needed.