The Persistent Concrete Bias in Monkey Reasoning

Humans in industrialized societies typically exhibit a relational bias, readily attending to patterns between objects (relative sizes or heights). In contrast, young children, adults without formal schooling, and non-human primates display a concrete bias, favoring absolute features (individual size or total amount). Whether this contrast reflects a true predisposition or a learning limitation remains unclear. To distinguish between these explanations, we presented rhesus macaques with a match-to-sample task that pitted concrete matches against relational matches, varying which option was reinforced. Monkeys first received non-differential feedback and preferred concrete matches. Then, we reinforced only relational matches, and they learned to select the relational option. Crucially, once feedback was removed, they reverted to concrete matching, indicating a persistent bias rather than a lack of learning opportunities. This suggests an inherent primate predisposition toward concrete processing that may be overridden by the cultural and educational influences of human societies, which favor relational processing.