To investigate the effects of various changes on the magnitude of the OR, two pairs of stimuli were used such that for each pair, each stimulus served as the repeated event for one group of Ss and as the altered event for another. It was predicted that stimulus change resulting in increased stimulus intensity would result in a larger OR than stimulus change resulting in decreased intensity. Chromatic and achromatic stimuli were used to test this hypothesis and the results confirmed this notion. The second set of stimuli, varying in contour, tested the hypothesis that changes independent of intensity should affect OR magnitude. The results support this view and suggest that the salience of the change in terms of the organism's hierarchy of interest must be included in a complete analysis of the magnitude of an OR.