All differences are not created equal: A structural alignment view of similarity

An emerging view in cognitive psychology is that the determination of similarity involves a comparison of structured representations. On this view, some differences are related to the commonalities of a pair (alignable differences) and others are unrelated to the commonalities of a pair (nonalignable differences). Previous evidence suggests that pairs of similar items have more commonalities and alignable differences than do pairs of dissimilar items. Structural alignment further predicts that alignable differences should be easier to find than nonalignable differences. Taken together, these assertions lead to the counterintuitive prediction that it should be easier to find differences for similar pairs than for dissimilar pairs. This prediction is tested in two studies in which subjects are asked to list differences for as many word pairs as possible in a short period of time. In both studies, more differences are listed for similar pairs than for dissimilar pairs. Further, similar and dissimilar pairs differ in the number of alignable differences listed for them, but not in the number of nonalignable differences listed for them. These studies provide additional support for the structural alignment view of similarity.