This paper examines the concept of decalage from two cognitive-change positions (structures of logical thought and attentional and verbal mediators) and proposes an alternative explanation for decalage from a perceptual-change point of view. The term decalage is used to summarize the relation between differences in performance of various age groups and differences in information contained in problem-solving tasks that have the same solution requirements. According to the cognitive change position, age-related performance differences are assumed to result from different cognitive structures that evaluate the same information. However, this position cannot adequately explain decalage relations such as 8-year-olds conserving mass while 10-year-olds cannot conserve volume. In the perceptual-change position, decalage relations are assumed to be a source of information about developmental changes in the perceptual system and how that system determines what information is processed by cognitive structures. Two studies are described in which the dimensional salience of task components was manipulated in order to assess the role of perception in tasks usually used to measure cognitive change (matrix solution and relevant versus incidental recall). The results were interpreted as showing that perceptual salience was a significant determinant of the obtained decalages and it was suggested that perceptual characteristics could explain decalages found in other cognitive-change research. (JMB)