In 1971, Shepard and Metzler described for the first time the psychological process of mental rotation. The classic paradigm to explore mental rotation consists in presenting pairs of tridimensional figures arranged in different orientations, and asking subjects to identify if both figures are identical or if, on the contrary, one of them is the symmetrical image of the other (its mirror image). In this task, it can be observed that the amount of time that is required by subjects to respond increases as the rotation angle gets bigger. This would imply that to give the right answer subjects must carry out a mental rotation process until both figures are placed in the same position. Mental rotation is a prototypical example of the processes studied in the mental imagery paradigm (for instance, see Kosslyn, 1994). The goal of the first experiments in this research field consisted in showing that mental representations, besides having a symbolic propositional format, could also have an analogical format whose properties were similar to those of a physical stimulus.
