IMAGE DISCRIMINATION MODELS PREDICT DETECTION IN FIXED BUT NOT RANDOMNOISE

By means of a two-interval forced-choice procedure, contrast detection thresholds for an aircraft positioned on a simulated airport runway s cene were measured with fixed and random white-noise masks. The term f ixed noise refers to a constant, or unchanging, noise pattern for each stimulus presentation. The random noise was either the same or differ ent in the two intervals. Contrary to simple image discrimination mode l predictions, the same random noise condition produced greater mashin g than the fixed noise. This suggests that observers seem unable to ho ld a new noisy image for comparison. Also, performance appeared limite d by internal process variability rather than by external noise variab ility, since similar masking was obtained for both random noise types. (C) 1997 Optical Society of America.