The uncertainty response has been influential in studies of human perception, and it is crucial in the growing research literature that explores animal metacognition. However, the uncertainty response's interpretation is still sharply debated. The authors sought to clarify this interpretation using the dissociative technique of cognitive loads…

The goal of the current research was to explore whether monkeys possess conceptual precursors necessary for understanding zero. We trained rhesus monkeys on a nonsymbolic numerical matching-to-sample task, and on a numerical ordering task. We then introduced nondifferentially reinforced trials that contained empty sets to determine whether monkeys…