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The Human Intruder Test: An Anxiety Assessment in Rhesus Macaques (Macaca Mulatta)

By Emily J. Peterson

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The human intruder test (HIT) is a noninvasive tool widely used for assessing anxiety in rhesus macaques (Macaca mulatta). This thesis explores the HIT procedure and applies it to a population of monkeys with a self-injurious behavioral pathology. Individual variation on this test can be used to assess anxiety and temperament. The first experiment of this thesis applied two different procedures of the HIT to 17 monkeys at UMass. Monkeys displayed little response to the intruder, and no significant differences were detected for the two procedures. To determine whether these responses were unique to the UMass monkeys, their behavior was then compared to the behavior of monkeys at three other primate facilities. UMass monkeys showed less of a reaction compared to monkeys at other facilities. They came to the front of the cage when the intruder entered the room whereas the monkeys at other facilities moved to the back and showed virtually no threats to the intruder. One possible explanation is the increased exposure to humans that UMass monkeys experience. Even though the human running the HIT was a stranger, monkeys at UMass may not perceive a new human in front of their cage to be a threat. The second experiment tested the hypothesis that monkeys with a record of self-injurious behavior (SIB) would be more anxious in response to the HIT. The cage-side version of the HIT was applied to 41 monkeys with a record of self-injurious behavior and 36 matched controls. In contrast to our prediction, SIB subjects spent significantly less time showing anxious behavior and aggressive behavior toward the intruder as well as spent more time in the front of the cage. SIB subjects showed the same range of behaviors as controls, but significantly less behavioral change overall. These data add to the evidence from experiment one that the HIT may not be a sufficient novelty test to elicit a response in monkeys who are more often exposed to different people. An alternative explanation is that SIB is associated with a depressive like syndrome based on reduced overall activity and possibly lowered affect during the stare phase.


Katie Carroll

Date 2015
Pages 1-45
Publisher University of Massachusetts-Amherst
Department Neuroscience and Behavior
Degree Master of Science
Language English
University University of Massachusetts-Amherst
Cite this work

Researchers should cite this work as follows:

  1. Animal behavior
  2. Animal roles
  3. Animal welfare
  4. Anxiety
  5. human-wildlife interactions
  6. Macaques
  7. Mammals
  8. Monkeys
  9. Nature
  10. Stress
  11. Wild animals