Nelson, E. E., Shelton, S. E., & Kalin, N. H. (2003). Individual differences in the responses of naive rhesus monkeys to snakes. Emotion, 3(1), 3–11.
Abstract: The authors demonstrated individual differences in inhibited behavior and withdrawal responses of laboratory-born rhesus monkeys when initially exposed to a snake. Most monkeys displayed a small significant increase in their behavioral inhibition in the presence of a snake. A few monkeys had marked responses, and some actively withdrew. Although the responses of the most extreme laboratory-born monkeys were comparable to feral-born monkeys, the responses of the laboratory-born monkeys rapidly habituated. The individual differences in the responses of naive monkeys likely reflect a continuum from orienting to wariness to fear. A neurobiological model is presented that addresses potential mechanisms underlying these individual differences, their relation to fear, and how they may predispose to phobia development.
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Capitanio, J. P. (1999). Personality dimensions in adult male rhesus macaques: prediction of behaviors across time and situation. Am. J. Primatol., 47(4), 299–320.
Abstract: The idea that consistencies in behavior exist over time and across situations underlies human personality research. Although several studies have examined personality in nonhuman primates, there are very few data showing the predictive power of personality factors. The goal of the present study was to determine whether personality dimensions, identified in adult male rhesus monkeys living in half-acre cages, predicted behavior in situations different from the one from which the dimensions were originally derived and at time points of up to 4.5 years after the original assessments. Four personality dimensions (Sociability, Confidence, Excitability, and Equability) were identified using psychometric procedures and were correlated with behaviors recorded in several situations: the animals' natal groups, during tests of behavioral responsiveness while in individual cages, in small stable and unstable social groups, while viewing stimulus videotapes, and during stable social dyads. Results indicated substantial predictability. Sociability reflected a greater tendency to engage in affiliative interactions. Confidence correlated with more aggressive behaviors and with behaviors that suggest less attractiveness. Animals high in Excitability were somewhat inconsistent in their social behavior, perhaps reflecting hyper-responsiveness to novel circumstances and thwarted opportunities for escape. Equability appeared to be related to a less aggressive, more passive, style of interaction. Excitability and Equability appear to reflect more stylistic components of social behavior, whereas Sociability and Confidence may be more content-based dimensions. Sociability was strongly related to size of kin network in the animals' natal groups, suggesting an important role for ontogeny in this dimension. These data suggest that a limited number of personality dimensions exist in adult male rhesus macaques, and that these dimensions have predictive power that is both long-term and cross situational.
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Coleman, K., Tully, L. A., & McMillan, J. L. (2005). Temperament correlates with training success in adult rhesus macaques. Am. J. Primatol., 65(1), 63–71.
Abstract: In recent years there has been a marked increase in awareness of issues involving the psychological well-being of nonhuman primates (NHPs) used in biomedical research. As a result, many facilities are starting to train primates to voluntarily cooperate with veterinary, husbandry, and research procedures, such as remaining still for blood draws or injections. Such training generally reduces the stress associated with these procedures, resulting in calmer animals and, ultimately, better research models. However, such training requires great investments in time, and there can be vast individual differences in training success. Some animals learn tasks quickly, while others make slower progress in training. In this study, we examined whether temperament, as measured by response to a novel food object, correlated with the amount of time it took to train 20 adult female rhesus macaques to perform a simple task. The monkeys were categorized as “exploratory” (i.e., inspected a novel object placed in the home cage within 10 sec), “moderate” (i.e., inspected the object within 10-180 sec), or “inhibited” (i.e., did not inspect the object within 3 min). We utilized positive reinforcement techniques to train the monkeys to touch a target (PVC pipe shaped like an elbow) hung on their cage. Temperament correlated with training success in this study (Pearson chi2=7.22, df=2, P=0.03). We easily trained over 75% of the animals that inspected the novel food (i.e., exploratory or moderate individuals) to touch the target. However, only 22% of the inhibited monkeys performed the task. By knowing which animals may not respond to conventional training methods, we may be able to develop alternate training techniques to address their specific needs. In addition, these results will allow us to screen monkeys to be assigned to research projects in which they will be trained, with the goal of obtaining the best candidates for those studies.
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Capitanio, J. P., & Widaman, K. F. (2005). Confirmatory factor analysis of personality structure in adult male rhesus monkeys (Macaca mulatta). Am. J. Primatol., 65(3), 289–294.
Abstract: Reports from different laboratories have suggested that nonhuman primates have somewhat similar dimensions of personality. To date, however, no attempts have been made to statistically replicate a specific factor structure. In the present report, two independent observers recorded the behavior of 58 adult male rhesus monkeys, and then rated the animals with the use of a 50-item personality instrument. A confirmatory factor analysis (CFA) of the ratings resulted in the replication of a previously described four-factor personality structure [Maninger et al., American Journal of Primatology 61:73-83, 2003]. The first two dimensions-Sociability and Confidence-showed strong loadings and are similar to Affiliation and Agency dimensions in humans. The remaining dimensions-Equability and Irritability-were less clear, and it is possible that additional traits will have to be identified before a more robust structure can be established for these dimensions.
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Brannon, E. M., & Terrace, H. S. (2000). Representation of the numerosities 1-9 by rhesus macaques (Macaca mulatta). J Exp Psychol Anim Behav Process, 26(1), 31–49.
Abstract: Three rhesus monkeys (Macaca mulatta) were trained to respond to exemplars of 1, 2, 3, and 4 in an ascending, descending, or a nonmonotonic numerical order (1-->2-->3-->4, 4-->3-->2--1, 3-->1-->4-->2). The monkeys were then tested on their ability to order pairs of the novel numerosities 5-9. In Experiment 1, all 3 monkeys ordered novel exemplars of the numerosities 1-4 in ascending or descending order. The attempt to train a nonmonotonic order (3-->1-->4-->2) failed. In Experiment 2A, the 2 monkeys who learned the ascending numerical rule ordered pairs of the novel numerosities 5-9 on unreinforced trials. The monkey who learned the descending numerical rule failed to extrapolate the descending rule to new numerosities. In Experiment 2B all 3 monkeys ordered novel exemplars of pairs of the numerosities 5-9. Accuracy and latency of responding revealed distance and magnitude effects analogous to previous findings with human participants (R. S. Moyer & T. K. Landaeur, 1967). Collectively these studies show that monkeys represent the numerosities 1-9 on at least an ordinal scale.
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