Measuring performance efficiency and consistency in visual discriminations with noisy images

These experiments measured the efficiency of disk discrimination performance, relative to an "ideal" observer, and compared 2 visually dissimilar tasks in which noisy image stimuli were identical for a physical calculation yielding optimum decisions. Performance consistency was measured by estimating the assumed underlying correlation in an observer's judgments about the same individual "frozen noise" images across independent replications of each condition. Larger disk sizes on the stimulus images considerably reduced observer performance efficiency (by a factor of 10) in both discrimination tasks, regardless of the image viewing distance. But even when efficiency was very low (5% or less), performance consistency still remained quite high (about 50%). About half of each observer's inefficiency appeared to reflect consistent (but suboptimal) perceptual "miscalculations" of the noisy stimulus information.