Wright, A. A., & Katz, J. S. (2006). Mechanisms of same/different concept learning in primates and avians. Behavioural Processes, 72(3), 234-254.

Mechanisms of same/different concept learning by rhesus monkeys, capuchin monkeys, and pigeons were studied in terms of how these species learned the task (e.g., item-specific learning versus relational learning) and how rapidly they learned the abstract concept, as the training set size was doubled. They had similar displays, training stimuli, test stimuli, and contingencies. The monkey species learned the abstract concept at similar rates and more rapidly than pigeons, thus showing a quantitative difference across species. All species eventually showed full concept learning (novel-stimulus transfer equivalent to baseline: 128-item set size for monkeys; 256-item set for pigeons), thus showing a qualitative similarity across species. Issues of stimulus regularity/symmetry, generalization from item pairs, and familiarity processing were not considered to be major factors in the final performances, converging on the conclusion that these species were increasingly controlled by the sample-test relationship (i.e., relational processing) leading to full abstract-concept learning. (c) 2006 Published by Elsevier B.V.