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William A. Simpson; Detecting simple patterns with night vision goggles. Journal of Vision 2004;4(8):788. doi: 10.1167/4.8.788.
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© ARVO (1962-2015); The Authors (2016-present)
Night vision goggles (NVGs) are widely used visual aids, particularly in night-time military operations. The purpose of this study was to see precisely how NVGs aid in the detection of simple patterns. Previous experiments in photopic conditions have shown that there are two factors that limit detection: sampling efficiency and internal noise. Ideally, the NVG might increase sampling efficiency and reduce internal noise. We measured the threshold contrast energy for detecting a Gabor patch in various levels of Gaussian white noise. The light delivered to the eye travelled through neutral density filters and an NVG. Several mean luminances were used. We find that for a mean luminance at the eye of 10 cd/m2, the observer using an NVG had a higher internal noise level and a lower efficiency than the observer using a naked eye. The NVG amplifies the light by a factor of 2600, though, so the interesting comparison is between a Gabor with mean luminance .0038 cd/m2 viewed with and without NVG. It turned out that the functional relationship between threshold energy and noise power spectral density broke down at low luminances, and so the internal noise/sampling efficiency scheme no longer held. Our evidence suggests instead that a hard threshold limits detection, and that NVGs work by lifting the pattern's contrast above a hard threshold.
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