Figure 5. Geometric Depiction of the Six Problem Types (Shepard et al., 1961).

Note. Members of each category are denoted by white and black spheres. In the Type I problem, a single dimension is relevant. In the Type II problem, two dimensions are relevant, and decisions makers must employ a logical XOR rule. In the Type III, IV, and V problems, all dimensions are informative, but the categorization structures differ in interesting ways. In the Type VI problem, all stimulus dimensions must be considered.