How special is sameness for pigeons and people?

Because of the importance of the sense of sameness for psychological science and because of the tenuous support for this notion in pigeons' matching-to-sample behavior, we experimentally explored the possibly special status of sameness for pigeons. Using photographs from three different natural categories (dogs, fish, and flowers) in a three-alternative matching-to-sample design, we obtained a reliable sameness advantage for pigeons only when the number of correct sample-comparison combinations could have contributed to a sameness advantage; otherwise, no sameness advantage emerged. However, human participants exhibited an immediate and dramatic sameness advantage under essentially the same training and testing conditions as had been given to pigeons. At least under these experimental circumstances, humans exhibit a sameness advantage that far eclipses that of pigeons.