Memory-basedsame-different conceptualization by pigeons

We first trained pigeons to peck one button (same) after the successive presentation of 16 identical pictures and to peck a second button (different) after the successive presentation of 16 nonidentical pictures. Later, we tested the birds with other lists ofsame anddifferent items composed of completely novel pictures. Accuracy to the testing lists reliably exceeded chance levels, thus demonstratingsame-different conceptualization by pigeons under conditions that, for the first time, (1) eliminated purely perceptual mechanisms of discrimination learning and transfer and (2) required memory-based processing of the experimental stimuli.