Figure 2.

Morph spaces used by Folstein et al. (2012), which include, in a) and b), the morph space used by Goldstone and Steyvers (2001), and in c) and d), the morph space used by Jiang et al. (2007). Both assume spaces that are created from four (roughly) equally dissimilar morph parents (A–D). These four parents occupy the corners of a tetrahedron in panels b) and d). Panels a) and c) show “flattened” versions of the spaces, separated by category boundaries used by the subjects during category learning. Panels b) and d) show the actual spaces situated within the tetrahedra. While the flattened two-dimension representations are strikingly similar, the actual spaces of morphs and their relationships to the learned category boundaries are quite different, with consequences on observed behavior, as outlined in the text.