The hypothesis that overall-similarity relations structure both adults' and children's classifications of heterogeneous objects (objects that differ in a variety of ways) was supported in two experiments. When objects varied simultaneously on many dimensions, adults and children constructed classifications that maximized within-category similarity…

Two experiments show that action alters the shape categories formed by 2-year-olds. Experiment 1 shows that moving an object horizontally (or vertically) defines the horizontal (or vertical) axis as the main axis of elongation and systematically changes the range of shapes seen as similar. Experiment 2 shows that moving an object symmetrically (or…