same-different; opposition; diversity; similarity; perceptually grounded relationships

After considering the pervasiveness of same/different relationships in Psychology and the experimental evidence of their perceptual foundation in Psychophysics and Infant and Comparative Psychology, the paper develops its main argument. Similarity and diversity do not complete the panorama since opposition constitutes a third relationship which is distinct from the other two. There is evidence of this in previous literature investigating the perceptual basis of opposition and in the results of the two new studies presented in this paper.