Three studies examined preschool children's understanding of categorical hierarchies, testing their ability to form categories at different levels of generality and to include the same objects in multiple categories. Found that, contrary to the implications of previous studies, two- and three-year olds appear to have both categorization skills.…

Two studies of development of spatial representation with two dimensions found that children as young as five years use the same two independent dimensions in fine-grained spatial coding of location in a circle as adults use--radius and angle. The adult pattern, where angle as well as radius is coded hierarchically, emerges by nine years. (HTH)