In four experiments, younger children and adults showed greater perceptual sensitivity and more extensive conceptual labeling for difference relations than for identity relations. Younger and older children demonstrated consistent dimensional selectivity in tasks involving free classification and the estimation of differences. (Author/BG)

Two experiments investigated perceptual primacy of dimensional and similarity relations in stimulus classifications of younger and older subjects. Results support a differential-sensitivity view of perceptual development which asserts that individuals at all ages primarily perceive and use separate relations. (RWB)