Entropy detection by pigeons: response to mixed visual displays after same-different discrimination training.

Pigeons were trained to peck 2 different buttons in response to 16-icon Same versus Different arrays. In Same arrays, the icons were identical to one another, whereas in Different arrays, the icons were different from one another. In Experiment 1, pigeons discriminated Same from Different arrays and transferred their discriminative responding to arrays of novel icons. In Experiments 2-4, pigeons exhibited sensitivity to the degree of display variability when shown intermediate Mixture arrays. Entropy, an information theoretic measure, systematically described these results while outperforming rival accounts.