up-and-down method

n. A method in psychophysics in which the limits of perceptual accuracy are discovered by presenting a series of stimuli ordered from strongest to weakest or weakest to strongest and the limen threshold is determined by the intensity of the stimulus at which responses change. For difference thresholds, the absolute difference between a stimulus and a comparison stimulus is adjusted up when the difference is not perceived or down when the difference is perceived until the difference at which response change is found. Also known as the staircase method.