No same–different concept or entropy stimulus control: Multiple-item array task performance in budgerigars (Melopsittacus undulatus) and pigeons (Columba livia).

To investigate same-different conceptualization in nonhuman animals, researchers have used the multiple-item array task (MIAT), which requires discriminating whether icons in an array are the same or different from one another. Although entropy-based explanations for MIAT performance have been influential, their validity is debatable. In Experiment 1, budgerigars and pigeons were trained to discriminate whether 16 icons were the same or different from one another. When the number of icons was reduced, the discrimination tendency of both species was correlated with the entropy value, replicating previous findings. Experiment 2 further supported this correlation by controlling for the number of icons and icon patterns. However, Experiment 3 revealed that when entropy was constant, the subjects judged different more frequently for arrays with more icons per pattern, which contradicts entropy-based predictions. Notably, the response patterns of the subjects in Experiment 3 were inconsistent with logical same-different judgments, suggesting that these animals perform the MIAT based on criteria distinct from those of same-different conceptualization. These findings challenge the validity of typical MIAT for examining same-different concepts in animals and indicate the need to develop more reliable alternative methods. (PsycInfo Database Record (c) 2025 APA, all rights reserved).