Effects of band-limited noise on human observer performance

Perception tests establish the effects of spatially band-limited noise and blur on human observer performance. Previously, Bijl showed that the contrast threshold of a target image with spatially band-limited noise is a function of noise spatial frequency. He used the method of adjustment to find the contrast thresholds for each noise frequency band. A noise band exists in which the target contrast threshold reaches a peak relative to the threshold for higher- or lowernoise frequencies. Bijl also showed that the peak of this noise band shifts as high frequency information is removed from the target images. To further establish these results, we performed forced-choice experiments. First, a Night Vision and Electronics Sensors Directorate (NVESD) twelve (12)-target infrared tracked vehicle image set identification (ID) experiment, second, a barpattern resolving experiment, and third, a Triangle Orientation Discrimination (TOD) experiment. In all of the experiments, the test images were first spatially blurred, then spatially band-limited noise was added. The noise center spatial frequency was varied in half-octave increments over seven octaves. Observers were shown images of varying target-to-noise contrasts, and a contrast threshold was calculated for each spatial noise band. Finally, we compared the Targeting Task Performance (TTP) human observer model predictions for performance in the presence of spatially band-limited noise with these experimental results.