The two researchers carried out their experiment on 29 baboons (Papio papio) of variable ages, which could freely perform the proposed exercise (this represents a large number of animals for this type of experiment). First of all, the baboons were shown two geometric shapes on a touch screen, for example two squares. After they touched one of these shapes, two other pairs of shapes appeared on the screen, such as: a triangle and a star for the first pair and two identical ovals for the second pair. To successfully complete the exercise and be rewarded, the animal had to touch the pair representing the same relation (of identity or difference) as the initial pair (here, the two ovals).