Fig. 2.

The two 4-member stimulus classes hypothesized to result from class merger via common elements after training on hue–form symbolic, hue identity, and form identity successive matching. Solid and dashed arrows denote explicitly trained and predicted emergent symbolic relations, respectively. R = red, G = green, T = triangle, H = horizontal, c = stimulus appearing on center key, l = stimulus appearing on left key, 1 = first ordinal position (sample stimulus), 2 = second ordinal position (comparison stimulus).