Evidence for a conceptual account of same-different discrimination learning in the pigeon.

We trained pigeons to peck two different buttons in response to 16-icon same arrays versus 16-icon different arrays. In the same arrays, the icons were all the same as one another, whereas in the different arrays, the icons were all different from one another. In Experiment 1, we upset the spatial regularities of the displays by disarranging the icons--randomly displacing each icon to reduce the degree of perceptual order. The pigeons' discriminative performance was unaffected by disarranging. In Experiment 2, spatial regularities were disturbed by varying the rotation of the icons within a display. Again, no disruption in discriminative performance was observed. These and other findings suggest that pigeons treat the 16 icons as either the same or different despite changes in the spatial organization or orientation of the icons, thus implicating a conceptual rather than a perceptual process in same-different discrimination.