Size Estimation with Night Vision Goggles
DEFENCE SCIENCE AND TECHNOLOGY ORGANISATION CANBERRA (AUSTRALIA)
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Human observers matched the size of a comparison disc object to the perceived size of a test disc located at between 1 and 6 m under normal daylight viewing and when viewing through night vision goggles NVGs under simulated starlight. The results showed that observers were more accurate at judging size with unaided vision than when viewing with NVGs. The results for unaided viewing were in accord with the law of size constancy that predicts that accurate size estimation is a result of observers taking into account the distance at which objects are located. The results for viewing with NVGs depart from size constancy and are influenced to a greater extent by the law of visual angle that predicts that size estimates are based more on the angular size of the target because there is inadequate distance information available in this condition. These results demonstrate that NVCs alter normal visual space perception and this should be taken into account in training aircrew and evaluating the effect of NVGs on flying performance. Our results are consistent with other results reported in the literature for longer observation distances.
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