International Journal of Comparative Psychology

Pigeons that had extensive training with an oddity-frona-sample discrimination procedure using visual patterns, and that could transfer their performance to novel patterns, were tested for three kinds of pattern recognition invariance. In one invariance experiment the sample stimuli were silhouette shapes and the comparison stimuli were outline figures. In another experiment the samples were white shapes on a dark background whereas the comparisons were black shapes on a bright background. In a third experiment the sample and comparison shapes were of different color. All the shapes used for invariance testing were novel to the pigeons. Performance during the tests was above 90% correct except in the case of the reversed contrast experiment, where it reached only 77/6; dazzling and/or attention problems may have been a disturbing factor. Even in this condition, however, significant transfer was obtained. Generally the pigeons showed that they are capable of invariant shape recognition under all three conditions. Since all critical tests involved shapes that were novel to the subjects the results also confirmed that pigeons can conceptualize a relational oddity/ identity rule.