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17 April 1995 Observer detection efficiency with target size uncertainty
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The effect of target size and size uncertainty on human observer ability to see disk targets in uncorrelated noise was measured. disk targets were centered in 64-pixel-radius areas of uncorrelated Gaussian noise. Human observers rated the likelihood that a target was present Size uncertainty was introduced in the target-present stimuli by using disk targets with radii ranging 2 to 33.2 pixels. A constant matched-filter signal-to-noise ration was maintained across the range of disk sizes by adjusting the disk contrast. For this mixed size experiment the observer ratings were analyzed using a multiple-distribution extension of the binormal ROC curve fitting procedure. A control experiment measured observer performance in conditions with target-present stimuli of known-size disks. A third experiment evaluated the influence of noise-area size on performance with known-size disks. An observer detection efficiency index, the square of the ration of d' to SNR, decreased at small and large disk radii. The efficiency index decrease for small disks was less in the control experiment (size- known). Observer efficiency indexes for medium and large disks were not significantly difference for the mixed size experiment and the control experiment. Reducing the noise-area size increased the efficiency for small disks and produced an approximately constant efficiency for the small to medium sized disks. Size uncertainty decreased observer detection performance relative to known-size performance for small disk targets. the observer efficiency index for the small targets was increased when small noise areas are used. This finding suggests that the decreased efficiency index for small targets on large noise areas was caused by increased observer uncertainty of target location.
© (1995) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Philip F. Judy, Marie Foley Kijewski, Xiaoyang Fu, and Richard G. Swensson "Observer detection efficiency with target size uncertainty", Proc. SPIE 2436, Medical Imaging 1995: Image Perception, (17 April 1995);

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