DOI 10.1007/s10071-008-0149-0ORIGINAL PAPER Inferential reasoning by exclusion in pigeons, dogs, and humans

Abstract The ability to reason by exclusion (which is deWned as the selection of the correct alternative by logi-cally excluding other potential alternatives; Call in Anim Cogn 9:393–403 2006) is well established in humans. Sev-eral studies have found it to be present in some nonhuman species as well, whereas it seems to be somewhat limited or even absent in others. As inconsistent methodology might have contributed to the revealed inter-species diVerences, we examined reasoning by exclusion in pigeons (n = 6), dogs (n = 6), students (n = 6), and children (n = 8) under almost equal experimental conditions. After being trained in a computer-controlled two-choice procedure to discrimi-nate between four positive (S+) and four negative (S¡) photographs, the subjects were tested with displays consist-ing of one S ¡ and one of four novel stimuli (S). One pigeon, half of the dogs and almost all humans preferred S over S¡, thereby choosing either by novelty, or by avoid-ing S ¡ without acquiring any knowledge about S, or by inferring positive class membership of S by excluding S¡. To decide among these strategies the subjects that showed a preference for S were then tested with displays consisting of one of the S and one of four novel stimuli (S). Although the pigeon preferentially chose the S and by novelty, dogs and humans maintained their preference for S, thereby showing evidence of reasoning by exclusion. Taken together, the results of the present study suggest that none of the pigeons, but half of the dogs and almost all humans inferred positive class membership of S by logi-cally excluding S¡