Animal Cognition

, Volume 7, Issue 4, pp 239–246 | Cite as

Rhesus monkeys (Macaca mulatta) discriminate between knowing and not knowing and collect information as needed before acting

  • Robert R. Hampton
  • Aaron Zivin
  • Elisabeth A. Murray
Original Article


Humans use memory awareness to determine whether relevant knowledge is available before acting, as when we determine whether we know a phone number before dialing. Such metacognition, or thinking about thinking, can improve selection of appropriate behavior. We investigated whether rhesus monkeys (Macaca mulatta) are capable of a simple form of metacognitive access to the contents of short-term memory. Monkeys chose among four opaque tubes, one of which concealed food. The tube containing the reward varied randomly from trial to trial. On half the trials the monkeys observed the experimenter baiting the tube, whereas on the remaining trials their view of the baiting was blocked. On each trial, monkeys were allowed a single chance to select the tube containing the reward. During the choice period the monkeys had the opportunity to look down the length of each tube, to determine if it contained food. When they knew the location of the reward, most monkeys chose without looking. In contrast, when ignorant, monkeys often made the effort required to look, thereby learning the location of the reward before choosing. Looking improved accuracy on trials on which monkeys had not observed the baiting. The difference in looking behavior between trials on which the monkeys knew, and trials on which they were ignorant, suggests that rhesus monkeys discriminate between knowing and not knowing. This result extends similar observations made of children and apes to a species of Old World monkey, suggesting that the underlying cognitive capacities may be widely distributed among primates.


Metacognition Metamemory Declarative Introspection Memory awareness 



We thank David Ide of Research Services Branch, National Institute of Mental Health, Bethesda, Maryland, for fabricating the apparatus, making critical contributions to the apparatus design, and taking the photos shown in Fig. 1. We thank Josep Call for encouragement, helpful discussions, and sharing unpublished data. These experiments comply with US law.


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Copyright information

© Springer-Verlag 2004

Authors and Affiliations

  • Robert R. Hampton
    • 1
  • Aaron Zivin
    • 1
  • Elisabeth A. Murray
    • 1
  1. 1.Section on the Neurobiology of Learning and Memory, Laboratory of NeuropsychologyNational Institute of Mental Health, NIHBethesdaUSA

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