The symbolic distance effect for alphabetic order judgements: A subjective report and reaction time analysis

The time needed to decide whether a pair of letters is in the correct alphabetic order varies inversely with alphabetic separation. This is an example of a phenomenon generally found with the comparison of ordered symbols or concepts, called the symbolic distance effect (Moyer and Bayer, 1976). It is argued that when letters are compared, an important determinant of this effect is the degree to which subjects subvocally run-through parts of the alphabet to determine the correctness of the order of a stimulus pair. A trial-by-trial introspection procedure coupled with reaction time measurements is used in the present experiment, in which letter order judgements were made over a range of separations. RTs increased with increasing number of letters in the reported run-through. At small letter separations, run-through occurred more frequently, and this was found to be the basis of the symbolic distance effect. For trials on which no run-through was reported the symbolic distance effect was absent. The data are summarized as a model in which comparisons are made from directly available order information from memory, or with an additional run-through process. The details of the run-through process suggest that groupings learned in childhood are probably involved in the selection of the starting letter for run-through.