A malamute-husky mixed-breed dog was trained to distinguish one object that differed from three others that were identical to each other. The dog progressed rapidly after an effective shaping procedure, requiring 37 training sessions to master 20 such problems to a criterion of 90 %. The dog subsequently scored 80 % correct on the first trials with new problems that required a reversal of previously correct choices. The dog then scored 70 % correct on his first trials with 20 new problems composed of entirely new objects. Both performances are far above chance. Consequently, we conclude that choosing the odd or least numerous object in a group is within the capacity of the domestic dog.
Keywords: Animals; Numerosity; Oddity; Stimulus relationships.