Positional discriminability in linear orderings

Subjects were taught two eight-term linear orders of the form “A taller than B taller than C ….,” They were then asked to choose the “taller” term in all possible pairwise combinations within each series, and reaction time was measured for each pair. In addition, subjects performed a further task in which they judged whether or not two terms were adjacent in the ordering. In subsequent sessions, subjects were told that the “shortest” term on one list was taller than the “tallest” term on the other, so that the two lists were merged into a single 16-term series. They were then required to choose the “taller” term for both within-groups and between-groups pairs. Subjects did not appear to use the initial groupings in performing this task, even when given training on differential categorical codes (“tall” vs. “short”) for the two sublists. Rather, subjects in all tasks appeared to represent the items as ordered positions along an internal array, so that comparison times depended largely on the differential discriminability of the item positions. In each task decisions were made more quickly if the terms being compared were near the ends of the ordering, rather than near the middle.