Comparative Perception and Attention Laboratory
Categories are often considered to be organized at multiple hierarchical levels, such as the subordinate, basic, and superordinate levels. The subordinate-level categories office chair and dining chair are included in the basic-level category chair which, in turn, is included in the superordinate-level category furniture. Some research has suggested that children learn to categorize first at the basic level (e.g., learning categories dog and cat before category animal), but others found faster learning for superordinate-level categories than for basic-level categories.
In my prior research that I have conducted at the University of Iowa in collaboration with Ed Wasserman and Fabian Soto, we hypothesized that between-category similarity may affect the speed of acquisition of basic-level and superordinate-level categories. Dissimilar categories may be easy to distinguish at the basic level but harder to group at the superordinate level, whereas similar categories may be easy to group at the superordinate level but difficult to distinguish at the basic level.
First, we experimentally evaluated the between-category similarity of four basic-level categories. We used the resultant similarity matrices in the next experiment to construct two superordinate-level categories from basic-level photographic categories with high between-category similarity (cars and persons; chairs and flowers). We then trained pigeons to concurrently classify those photographs into either the proper basic-level category or the proper superordinate-level category. Under these conditions, the pigeons learned the superordinate-level discrimination faster than the basic-level discrimination, confirming our hypothesis that basic-level superiority is affected by between-category similarity.
Lazareva, O.F., Soto, F., & Wasserman, E. A. (2010). Effect of between-category similarity on basic-level superiority in pigeons. Behavioural Processes, 85, 236-245. doi: doi:10.1016/j.beproc.2010.06.014