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The rationale was to apply Piaget's theory and methods to the study of the phylogenetic development of cognitive abilities. It was asked whether squirrel monkeys have the prerequisite skills for conservation of quantity, and, specifically, whether they might respond differentially to equivalent and unequivalent volumetric cues. All monkeys responded significantly and differentially to pairs of identical objects or pairs of objects similar only in volume vs. pairs of objects which differed in volume. It was concluded that squirrel monkeys have the prerequisite skills for the conservation of quantity. Discussion included methodological problems associated with demonstrating conservation in nonhumans as well as the potential usefulness of Piaget's theory for phylogenetic studies of intelligence. [ABSTRACT FROM AUTHOR]

Four squirrel and four Cebus monkeys were trained on five-trial oddity problems. Two of each species were then given problems where the odd object was reversed randomly on Trials 2, 3, or 4. They were then given one-trial oddity problems. All reached criterion in initial training. One Cebus reached criterion in reversal training, but the others showed significant improvement. All monkeys receiving one-trial oddity training responded correctly on 80% of 40 consecutive problems within 80 problems. No reliable differences were seen between the species. Discussion concerned the measures required to conclude that an animal has the oddity principle, and it was suggested that no nonprimate has been shown to master oddity. [ABSTRACT FROM AUTHOR]