Why is the alphabetically middle letter in a multiletter array so hard to determine? Memory processes in linear-order information processing

In 3 experiments, participants identified target letters in multiletter strings of different interletter steps. Results show that the alphabetically extreme targets in the arrays (A or C in BCA) were consistently identified faster than were the interior letters, with the alphabetically middle target (B in BCA) identified most slowly. Distance effects were not consistent across different targets. The findings are not consistent with the ends-inward serial search, comparison, and serial search plus comparison models. The data suggest that an interior target was identified by first identifying the terminal letter and then mentally constructing the linear order inward by probabilistically using either a comparison or an interitem serial search process to achieve maximal efficacy. This suggestion is consistent with the ends-inward construction theory of linear-order learning.