Discrimination of cartoons and photographs in pigeons: effects of scrambling of elements.

Four groups of pigeons were trained on four visual discrimination tasks using people photographs, pigeon photographs, cartoons of people, and cartoons of pigeons. After completion of the discrimination, the subjects were tested with new stimuli in the same stimulus categories but never used during the training, and scrambled stimuli in which elements of the original stimulus were spatially randomized. The subjects showed generalization to the new stimuli except for the people cartoons. When scrambled stimuli were presented, the subjects showed suppression of responding to the photographs but not to the people cartoon. These results suggest that the pigeons recognized both the elements and spatial arrangement of the photographs but ignored the spatial arrangement of the human cartoons.