Automatic comparisons of artificial digits never compared: learning linear ordering relations.

In 2 experiments, participants were trained to perform magnitude decisions, that is, decide which of 2 arbitrary symbols in a pair represented a larger magnitude. The symbols corresponded to locations on an implicit linear scale. Training resulted in a Stroop-like size congruity effect when the participants had to decide which symbol in a pair was physically larger. This effect, showing automaticity of the processing of magnitude relations, was also obtained for pairs never encountered during practice. The implications of these findings for processing of magnitude relations and for theories of automaticity are discussed.