What is the tree structure of personality?

Personality characteristics have been examined in a broad range of nonhuman species including chimpanzees, rhesus monkeys, ferrets, hyenas, rats, sheep, rhinoceros, hedgehogs, zebra finches, garter snakes, guppies, and octopuses [for a full review, see Gosling, 2001]. Such research is important because animal studies can be used to tackle questions that are difficult or impossible to address with human studies alone. By reaping the benefits of animal research, a comparative approach to personality can enrich the field of human personality psychology, providing unique opportunities to examine the biological, genetic, and environmental bases of personality, and to study personality development, personality-health links, and personality perception. However, all of these benefits hinge on the tenability of the personality construct in non-human animals. Thus, the purpose of the present paper is to address a key question in the animal domain: is personality real? That is, do personality traits reflect real properties of individuals or are they fictions in the minds of perceivers?

Thirty years ago, the question of the reality of personality occupied the attention of human-personality researchers, so our evaluation of the comparative approach to personality draws on the lessons learned in the human domain. Mischel’s [1968] influential critique of research on human personality was the first of a series of direct challenges to the assumptions that personality exists and predicts meaningful real-world behaviors. Based on a review of the personality literature, Mischel [1968] pointed to the lack of evidence that individuals’ behaviors are consistent across situations [Mischel & Peake, 1982]. Over the next two decades, personality researchers garnered substantial empirical evidence to counter the critiques of personality. In an important article, Kenrick and Funder [1988] carefully analyzed the various arguments that had been leveled against personality and summarized the theoretical and empirical work refuting these arguments.

The recent appearance of studies of animal personality has elicited renewed debate about the status of personality traits. Gosling, Lilienfeld, and Marino [in press] proposed that the conditions put forward by Kenrick and Funder [1988] to evaluate the idea of human personality can be mobilized in the service of evaluating the idea of animal personality. Gosling et al. [in press] used these criteria to evaluate research on personality in nonhuman primates. In the present paper, we extend their analysis to the broader field of comparative psychology, considering research on nonhuman animals from several species and taxa. Kenrick and Funder’s paper delineates three major criteria that must be met to establish the existence of personality traits: [1] assessments by independent observers must agree with one another; [2] these assessments must predict behaviors and real-world outcomes; and [3] observer ratings must be shown to reflect genuine attributes of the individuals rated, not merely the observers’ implicit theories about how personality traits covary. Drawing on evidence from the animal-behavior literature, we evaluate whether these three criteria have been met with respect to animal personality.

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• Do you see what I see? Investigating the validity of an equine personality questionnaire

  2022, Applied Animal Behaviour Science

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  Subjective equine personality questionnaires have the potential to predict a range of industry-relevant outcomes including fear reactivity, compliance with human cues, pain expression and susceptibility to stereotypies, in a time- and cost-efficient manner. However, to produce meaningful measures of target animals’ behavioural tendencies, subjective personality assessment tools must satisfy four criteria: internal consistency, predictive validity, inter-rater reliability, and test-retest reliability. The Equine Personality Test [EPT] has been developed to assess horses on five personality factors based on trait ratings from a familiar observer. While the EPT has been shown to have predictive validity, it has not been assessed for internal consistency, inter-rater reliability or test-retest reliability. To this end, three experienced primary caregivers and three riding instructors assessed 25 familiar horses using the EPT. The internal consistency, inter-rater reliability and test-retest reliability of the five subscales of the EPT were investigated using Cronbach’s α and intra-class correlation [ICC] analyses. The Agreeableness, Neuroticism, Extroversion and Gregariousness towards People subscales had high Cronbach α and inter-rater and test-retest ICC coefficients [α > 0.7; ICC>0.8]. By contrast, the Gregariousness towards Horses subscale had low Cronbach α [α = 0.39] and inter-rater ICC coefficient [ICC=0.498], and an adequate test-retest ICC coefficient [ICC=0.784]. Primary caregivers had higher ICC coefficients than instructors for most subscales and questionnaire items. The EPT therefore provides internally consistent and highly reliable measures of Agreeableness, Neuroticism, Extroversion, and Gregariousness towards People in equines, although measures of Gregariousness towards Horses should be interpreted with caution. The reliability of EPT scores can be further improved by targeting primary caregivers as raters. Taken together with previous findings demonstrating predictive validity for the questionnaire, these results contribute to making the EPT the only subjective equine personality questionnaire to have been checked against all four criteria of a valid and reliable personality assessment tool. This positions the EPT as a highly relevant equine personality assessment tool that may be used to predict behavioural tendencies in industry or research settings alike.

• Attention towards a handler in behavioural tests contributes to low ‘Distraction’ in guide dogs

  2022, Applied Animal Behaviour Science

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  Guide dogs are one type of assistance dogs in Japan that help individuals who are visually impaired. The qualification of candidate dogs is judged based on temperament and health. Previously, our group showed that ‘Distraction’ was the most influential behavioural trait for qualification at the Japan Guide Dog Association [JGDA]. In this study, to examine the underlying behavioural sub-traits associated with ‘Distraction’, we conducted behavioural tests focusing on the overall activity of candidate dogs and the degree to which they paid attention to a handler. The subjects were 59 candidate guide dogs [Labrador Retrievers] born and reared at the JGDA. At 7 weeks of age, we measured behavioural responses under the following situations: Isolation [5 min], Experimenter Entering [5 min], Elevation [30 s], and Restraint [30 s]. At 14 months of age [during the second month of training], we measured behavioural responses and physiological responses [heart rate] under the following situations: Kennel [10 min], Isolation [5 min], and Experimenter Entering [5 min]. When the dogs were 15 months of age [during the third month of training], we asked experienced trainers to complete a questionnaire to calculate the ‘Distraction’ score. We used multiple regression analysis [MRA] to examine the association between the ‘Distraction’ score, behavioural responses, and physiological responses at 7 weeks and 14 months of age. We found that dogs with lower ‘Distraction’ scores, i.e., less distractable, spent more time engaged in “struggle” behaviour in the Elevation condition at 7 weeks of age. At 14 months of age, they spent less time engaged in “active movement” and had a higher heart rate in the Isolation condition, and they spent more time engaged in “gaze” behaviour in the Experimenter Entering condition. According to the coefficient of determination and the standardized coefficients in the MRA, “gaze” in the Experimenter Entering condition had a comparatively large effect. Therefore, attention towards a handler, interpreted as “gaze”, appears to be an important underlying behavioural sub-trait for ‘Distraction’ compared with overall activity. These findings are expected to contribute to improving the training efficiency of guide dogs through the modification of both the training and breeding strategy.

• Personalized dominance – a questionnaire-based analysis of the associations among personality traits and social rank of companion dogs

  2022, Applied Animal Behaviour Science

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  In case of social animals often we can observe dominance hierarchies among the group members around limited resources. Once stabilized, hierarchy can help the access to these resources – in favour of the dominant individuals – without serious conflict or harm. While we can easily identify the limited resources in nature, in case of companion dogs, all essential resources are provided by the owner thus shortcutting competition. While it seems that its original function is not present in companion dogs, dominance hierarchies were still described in dog groups. As everyday competition for essential resources is seldom part of the lives of most companion dogs, our aim was to find what traits might be related to the formation of these hierarchies and the rank of the individuals. We designed an online survey for owners of multiple dogs to assess i] the dominance relationship between the co-habiting dogs via their everyday interactions and ii] their personalities using the Canine Big Five questionnaire. We received responses for 1082 dogs. Four of the five personality traits had a significant association with dominance: while more extroverted [p = 0.0003], conscientious [p = 0.0006], and open [p = 0.0088] dogs scored higher on dominance, more agreeable dogs scored lower [p  0.77, P  0.72, P