ABSTRACT
BACKGROUND: Binocular night vision goggles that have a monocular symbology overlay provide potential conflicts between perceived symbology distance and optical vergence cues for accommodation. HYPOTHESIS: Accommodative response was measured in subjects who perceived symbology nearer than the background to determine if accommodation could respond to the optical stimulus and override the perceptual cues. METHODS: Symbology was presented to the right eye under two conditions (clear and blurred to 20/50 resolution) and the background was presented binocularly with and without added speckle noise that is typical of the NVG at low light levels. RESULTS: On average, subjects accommodated by less than 0.1 diopters (D) to all 4 of the stimulus combinations even though the perceived proximal depth difference between background and symbology was 10 times greater. No perceptible blur resulted from this small change in accommodation because it is well below the depth of focus of the human eye. A control experiment illustrated that an accommodative response, at least as small as 0.25 D, could easily be stimulated optically and detected by the experimental apparatus. In a final experiment, the duration required to shift attention away from the background to a peripheral symbol, acquire critical information, and return attention to the background was 0.69 s which included saccade latency and scan time of the symbol. CONCLUSIONS: These results indicate that small changes in accommodation that occur when pilots shift attention from background to symbology do not produce perceived blur of the symbology or the background and thereby do not impair performance.
Subject(s)
Accommodation, Ocular/physiology , Attention/physiology , Data Display/standards , Sensory Aids/standards , Task Performance and Analysis , Vision, Binocular/physiology , Vision, Monocular/physiology , Adolescent , Adult , Darkness , Distance Perception/physiology , Evaluation Studies as Topic , Eye Movements/physiology , Female , Humans , Male , Optics and Photonics/instrumentation , Reaction Time/physiology , Visual Fields/physiologyABSTRACT
The PAVE LOW III aircraft is a modified HH-53H helicopter that has a low altitude--below 30.48 m (100 ft)--night/day rescue mission. The desired night flying configuration is for the pilot to wear night vision goggles (NVGs) to fly the aircraft while the copilot, without NVGs, observes the video display and monitors the aircraft instruments. The problems of NVG incompatibility in the cockpit were successfully countered using several light control techniques. The light control modifications were evaluated on the ground in the PAVE LOW III helicopter at Kirtland AFB in April, 1980, by PAVE LOW instructor pilots. The evaluation results were extremely positive.
