Top : Schematic of the three types of stimuli used: signs, colored disks, and geometrical forms. The objective of training was to form three classes of stimuli, with each class consisting of one sign, one color, and one geometrical form. Middle: Training related a stimulus from type A to a stimulus from type B, the A → B relations, and a stimulus from type B to a stimulus from type C, the B → C relations (solid arrows). All other relations among the stimuli were not trained (punctuated arrows). Instead, they were tested. Bottom: Sequence of relations trained and tested. Numbers refer to the arrows in the middle display.