Processing of order information for numbers and months.

Despite a great deal of research on the processing of numerical magnitude (e.g., the quantity denoted by the number 5), few studies have investigated how this magnitude information relates to the ordinal properties of numbers (e.g., the fact that 5 is the fifth integer). In the present study, we investigated order-related processing of numbers, as well as months of the year, with a novel ordering task to see whether the processing of order information differs from the processing of magnitude information. In Experiments 1 and 2, participants were shown three numbers (Experiment 1) or three months (Experiment 2) and were required to indicate whether the stimuli were in the correct order. In Experiment 3, participants were again shown three numbers; however, now they were instructed to indicate whether the three numbers were ordered in a forward, backward, or mixed direction. Whereas number comparison tasks typically reveal distance effects (comparisons become easier with increased distance between two numbers), these three experiments reveal a different pattern of results. There were reverse distance effects when the stimuli crossed a boundary (i.e., when numbers crossed a decade or months crossed the year boundary) and no effect of distance when the stimuli did not cross a boundary (i.e., when numbers were within a decade and months were within the January-December calendar year). These data suggest that additional mechanisms are involved in the processing of order information: a scanning mechanism and a long-term memory checking mechanism.