Are Line Lengths Critical to the Discrimination of Axisymmetric Pairs of Figures from Disoriented Identical Pairs?

I examined whether the lack of a difference in line lengths made the discrimination of axisymmetric (Ax) pairs of figures from disoriented identical (Idr) pairs difficult. Three basic pair types were prepared: Idr, Ax, and nonidentical/nonaxisymmetric (Nd) pairs. To avoid confusion arising from structural differences, all pairs of figures were set to be mutually isomorphic. Two figures of a pair were controlled to have the same line lengths of respective figural components (Experiment 1) or the same lengths of individual line segments (Experiment 2) in experiments where participants decided if the figures were the same/different. Experiment 1 showed longer latencies for Ax pairs than for Nd pairs, indicating that these feature values alone did not cause difficulty in discrimination. Experiment 2 showed that only Nd pairs with all line segments having the same lengths for the two figures had the same latencies as Ax pairs. The sameness of individual line segments in simple pairs of figures made discrimination difficult.