Mild hypoxia and visual performance with night vision goggles.

Military night vision goggles (NVGs) are image intensifiers normally used when the human operator's visual capabilities are unimpaired by oxygen deprivation. However, mountain search team members and aviators sometimes operate with NVG augmentation at altitudes where hypoxic visual decrement is documented. The objective of this research was to investigate the effects of mild hypoxia on monocular visual performance with NVGs. It was found that mild oxygen deprivation significantly affects unaided square-wave grating visual acuity but does not significantly affect NVG-augmented performance. Large differences between visual sensitivities at different spatial frequencies were not differentially affected by mild hypoxia. Supplemental oxygen did significantly improve naked-eye but not NVG-augmented night resolution acuity up to a simulated altitude of 13,000 ft (3,962 m) above sea level (ASL).

The moon illusion revisited.

In two experiments, the apparent size of a simulated horizon moon was measured as a function of the location of visible texture in the natural vistas against which it appeared. Size was found to increase as the visible scene extended farther into the distance and to decrease as the moon rose above the vista of surface texture. In the second experiment, the observers' eye accommodation distances to various scenes were also measured with a laser optometer, and after appropriate transformations, size judgments were found to correlate 0.89 with measured accommodation values, thereby suggesting the hypothesis that the fabled moon illusion is mediated by the oculomotor adjustments of visual accommodation.

Landing airplanes, detecting traffic, and dark focus.

Misjudgments of position in flight and failures to detect other airborne traffic are casualties of the eternal tug-of-war between visible texture and the pilot's dark focus. The eye is lazy and resists the pull of a distant stimulus, preferring to rest at a relatively short focal distance, as it does in the dark or when looking at the sky. Judgments of apparent size are highly correlated with visual accommodation distance, and the difficulty of detecting airplanes on stationary collision courses is greatly aggravated when focus is trapped by structure close to the eyes. Subject, cockpit design, task, and environment variables all interact to determine what we think we see.