Detecting variety: What's so special about uniformity?

Abstract

People and pigeons were taught to make 1 of 2 responses to 16-icon arrays that differed in their visual variability. In 2 experiments, participants had to (a) discriminate a collection of identical items from a collection in which 2 or more items were different or (b) discriminate a collection of different items from a collection in which 2 or more items were identical. In Experiment 1, humans found it much easier to discriminate uniformity from all levels of diversity. In Experiment 2, pigeons also found it easier to discriminate uniformity from all levels of diversity, but the size of this effect was smaller than that observed in people. These and other results suggest that both species are predisposed to notice differences rather than similarities.